Empirical support for "The Great Porn Experiment" - TEDx Glasgow (2012): Page 1

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Introduction

This page, and a second page, provide empirical support for claims put forth in The Great Porn Experiment | Gary Wilson | TEDxGlasgow. Each PowerPoint slide and associated text is accompanied by (1) the original supporting citations/sources, followed by (2) supporting studies and clinical evidence published in the intervening years. Slides 1 through 17 are below. This second page contains slides 18 through 35.

It’s important to note that The Great Porn Experiment was completed and sent to TEDx in December 2011, while the talk was given in March, 2012. This TEDx talk was a direct response to Philip Zimbardo's "Demise of Guys" TED talk, which the Glasgow audience viewed just prior to the talk.

Since December 2011, a large body of supporting research and clinical evidence has arrived to support The Great Porn Experiment's three primary assertions, which were:

  1. Internet porn can cause sexual dysfunctions;
  2. Internet porn use can lead to the 3 major addiction-related brain changes identified in substance addictions; and
  3. Internet porn use may exacerbate certain mental and emotional conditions (concentration problems, social anxiety, depression, etc.).  

The following is a short summary of empirical and clinical evidence supporting claims made in The Great Porn Experiment. Scroll down below it for slide-by-slide support.

1) Internet porn use can cause sexual dysfunctions:

2) Internet porn use can lead to the 3 major addiction-related brain changes identified in substance addictions:

The Great Porn Experiment listed ten internet addiction “brain studies,” which supported my thesis that internet addiction (and internet addiction subtypes such as gaming and porn) exists and involves the same fundamental mechanisms and brain changes as other addictions. This field of study is growing exponentially. As of 2017, there are some 250 internet addiction "brain studies." All of them report neurological findings and brain changes in internet addicts consistent with the addiction model (the list of Internet addiction "brain studies"). In addition, the design of several internet addiction studies supports the claim that internet use is causing (in some) symptoms such as depression, ADHD, anxiety, etc. The list of such studies: Studies demonstrating Internet use & porn use causing symptoms & brain changes.

The Great Porn Experiment described three major brain changes that occur with porn addiction: (1) Sensitization, (2) Desensitization, and (3) Dysfunctional prefrontal circuits (hypofrontality). Since March, 2012, much neurological research on porn users and porn addicts has been published. All three of these brain changes have been identified among the 37 neuroscience-based studies on frequent porn users and sex addicts:

  • Studies reporting sensitization or cue-reactivity in porn users/sex addicts: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20.
  • Studies reporting desensitization or habituation in porn users/sex addicts: 1, 2, 3, 4, 5, 6.
  • Studies reporting poorer executive functioning (hypofrontality) or altered prefrontal activity in porn users/sex addicts: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13.

The 37 neuroscience-based studies (MRI, fMRI, EEG, neuropsychological, hormonal) provide strong support for the addiction model, as do the 13 recent literature reviews by some of the top neuroscientists in the world.

I also described escalation or habituation in my TEDx talk (which can be an indication of addiction). Three studies have now asked porn users specifically about escalation into new genres or tolerance, confirming both (1, 2, 3). Employing various indirect methods, an additional 16 studies have reported findings consistent with habituation to "regular porn" or escalation into more extreme and unusual genres.

Finally, it wasn’t until 2017 that two research teams asked internet-porn users directly about withdrawal symptoms. Both reported withdrawal symptoms in “problematic porn users” (1, 2).

What about neurological studies that debunk porn addiction? There are none. While the lead author of Prause et al., 2015 claimed her lone EEG study falsified pornography addiction, six peer-reviewed papers disagree: 1, 2, 3, 4, 5, 6. The neuroscientists on these six papers state that Prause et al. actually found desensitization/habituation (consistent with the development of addiction), as less brain activation to vanilla porn (pictures) was related to greater porn use. Unbelievably, the Prause et al. team boldly claimed to have falsified the porn addiction model with a single paragraph taken from this 2016 "letter to the editor." In reality the Prause letter falsified nothing, as this extensive critique reveals: Letter to the editor “Prause et al. (2015) the latest falsification of addiction predictions" (2016).

But ‘porn addiction’ isn’t in the APA's DSM-5, right? When the APA last updated the manual in 2013 (DSM-5), it didn’t formally consider “internet porn addiction,” opting instead to debate “hypersexual disorder.” The latter umbrella term for problematic sexual behavior was recommended for inclusion by the DSM-5’s own Sexuality Work Group after years of review. However, in an eleventh-hour “star chamber” session (according to a Work Group member), other DSM-5 officials unilaterally rejected hypersexuality, citing reasons that have been described as illogical.

Just prior to the DSM-5’s publication in 2013, Thomas Insel, then Director of the National Institute of Mental Health, warned that it was time for the mental health field to stop relying on the DSM. Its "weakness is its lack of validity," he explained, and "we cannot succeed if we use DSM categories as the "gold standard." He added, "That is why NIMH will be re-orienting its research away from DSM categories." In other words, the NIMH planned to stop funding research based on DSM labels (and their absence).

Major medical organizations are moving ahead of the APA. The American Society of Addiction Medicine (ASAM) hammered what should have been the final nail in the porn-addiction debate coffin in August, 2011, a few months before I prepared my TEDx talk. Top addiction experts at ASAM released their carefully crafted definition of addiction. The new definition makes some of the major points I made in my talk. Foremost, behavioral addictions affect the brain in the same fundamental ways as drugs do. In other words, addiction is essentially one disease (condition), not many. ASAM explicitly stated that sexual behavior addiction exists and must necessarily be caused by the same fundamental brain changes found in substance addictions.

The World Health Organization appears poised to set right the APA’s excessive caution. The next edition of its diagnostic manual, the ICD, is due out in 2018. The beta draft of the new ICD-11 includes a diagnosis for “Compulsive sexual behavior disorder,” as well as one for “Disorders due to addictive behaviors.”

3) Internet porn use may exacerbate certain mental and emotional conditions

The Great Porn Experiment described “The Other Porn Experiment” in which young men who eliminated porn use reported remission of emotional and cognitive problems. TGPE also described "arousal addiction" (internet addiction and its subtypes) exacerbating or causing symptoms such as brain fog, concentration problem, generalized anxiety, depression and social anxiety. As of 2017 there exist hundreds of correlative studies and a few dozen causation studies supporting this assertion.

Note: some of the links are to versions of the studies that appear on www.yourbrainonporn.com. Links there, lead to abstracts and full studies elsewhere.


POWERPOINT SLIDES 1-17 & ASSOCIATED TEXT


SLIDE 1

The widespread use of Internet porn is one of the fastest moving, most global experiments ever unconsciously conducted.

ORIGINAL SUPPORT:

Common sense. Before the internet it was rare for those under 18 to have unfettered access to hard-core pornographic videos. The experiment gained momentum with the invention of porn tube sites (2006), and Smartphones (2008), and now VR porn.

UPDATED SUPPORT:

The Impact of Internet Pornography on Adolescents: A Review of the Research (2012) - An excerpt:

The recent proliferation of Internet-enabled technology has significantly changed the way adolescents encounter and consume sexually explicit material.

Sexual Media and Childhood Well-being and Health (2017) - Excerpts:

Sexual content is highly prevalent in traditional media, and portrayals rarely depict the responsibilities and risks (eg, condom use, pregnancy) associated with sexual activity. Exposure to such content is linked with shifts in attitudes about sex and gender, earlier progression to sexual activity, pregnancy, and sexually transmitted infection among adolescents. However, little information is available about moderators and mediators of these effects. We also know little about digital media, their sex-related content, and their potential influence on youth. Data from a few studies of older youth indicate that sexual displays on social media sites are related to problematic beliefs and behaviors among those who post this content and among viewers. Online pornography appears to be more problematic for youth than off-line sources. Given the vast and increasing amount of time youth spend online and their developmental openness to influence, more research attention to digital sexual media is needed.

Online Pornography: A Special Case. New technologies have expanded adolescents’ access to pornography. Online pornography differs from the pornography of the past in some critically important ways. Online content is always “on” and is portable, allowing access at any time and in any place. It can be interactive and more engaging, so there is potentially increased learning and exposure time. Extreme forms of violent or sexual content are more prevalent on the Internet than in other popular media. Participation is private and anonymous, which allows children and adolescents to search for materials they could not search for in traditional media. Finally, online media exposure is much more difficult for parents to monitor than media exposure in traditional venues. National and international studies reveal that exposure to online pornography is common among boys and not uncommon among girls.


SLIDE 2

Nearly every young guy with Internet access becomes an eager test subject.

ORIGINAL SUPPORT:

Just stating the obvious: streaming internet porn is available to every young man with Internet access.

UPDATED SUPPORT:

Rates of porn use have continued to rise. This 2017 study on Australians ages 15-29 found that 100% of the men had viewed porn. It also reported that increased pornography viewing frequency correlated with mental health problems.

This 2017 Swedish study reported that 98% of 18-year old males had watched pornography (The Relationship between Frequent Pornography Consumption, Behaviors, and Sexual Preoccupancy among Male Adolescents in Sweden). An excerpt from the study:

Our findings show that frequent users more often report behaviours associated with sexual risk taking including earlier age at sexual debut, anal sex, and having tried acts seen in pornography..... Based on the 3AM, if frequent users are more likely to test out sexual acts seen in pornography, it is not far-fetched to presume that the risky manner in which they have seen the acts performed might also be internalized (acquired) and applied (application) in real-life scenarios.

Results indicate that frequent users of pornography have sexual debuts at younger ages, engage in a broader range of sexual encounters, and are more likely to struggle with sexual preoccupancy and problematic pornography use. This study contributes to a growing body of research providing evidence that pornography may have negative effects on adolescents.


SLIDE 3

 

Canadian researcher Simon Lajeunesse found most boys seek pornography by age 10 - driven by a brain that is suddenly fascinated by sex. Users perceive Internet porn as far more compelling than porn of the past. Why is that? Unending novelty.

ORIGINAL SUPPORT:

Age boys seek pornography: Original article on Science Daily, where Lajeunesse said that most boys seek out pornography by age 10. It must be noted that Lajeunesse was asking twenty-somethings in 2009 to recall what had occurred 10-15 years earlier (mid to late 1990's), in an era when few young men possessed their own computer and everyone had dial-up.

Internet porn is more compelling due to novelty and other factors:

1) Studies reporting that pornographic films are more arousing than other types of pornography:  

2) Hundreds of animal and human studies have established that novelty is rewarding and increases mesolimbic dopamine. A few recent studies:

Novelty Seeking and Drug Addiction in Humans and Animals: From Behavior to Molecules (2016) - An excerpt:

On the molecular level, both novelty seeking and addiction are modulated by the central reward system in the brain. Dopamine is the primary neurotransmitter involved in the overlapping neural substrates of both parameters.

Neurotransmitters and Novelty: A Systematic Review (2016) - An excerpt:

Our brains are highly responsive to novelty. Here, we systematically review studies on human participants that have looked at the neuromodulatory basis of novelty detection and processing. While theoretical models and studies on nonhuman animals have pointed to a role of the dopaminergic, cholinergic, noradrenergic and serotonergic systems, the human literature has focused almost exclusively on the first two. Dopamine was found to affect electrophysiological responses to novelty early in time after stimulus presentation....

Dopamine Modulates Novelty Seeking Behavior During Decision Making monkeys (2014) - An excerpt:

The idea that dopamine modulates novelty seeking is supported by evidence that novel stimuli excite dopamine neurons and activate brain regions receiving dopaminergic input. In addition, dopamine is shown to drive exploratory behavior in novel environments.

Novelty increases the mesolimbic functional connectivity of the substantia nigra/ventral tegmental area (SN/VTA) during reward anticipation: Evidence from high-resolution fMRI (2011) - An excerpt:

We demonstrate that distinct clusters within the caudal portion of the medial SN/VTA and the lateral portion of the right SN are predominantly modulated by the anticipation of reward, while a more rostral part of the medial SN/VTA was exclusively modulated by novelty.

UPDATED SUPPORT:

While it's very difficult to establish the average age males first seek out internet pornography, the age of first access is dropping. For example, a 2008 study reported that 14.4 percent of boys were exposed to porn prior to age 13. By the time stats were gathered in 2011, early exposure had jumped to 48.7 percent. A 2017 cross-sectional study of Australians age 15-29 reports that 69 percent of males and 23 percent of females first viewed porn at age 13 or younger. All of the males and 82 percent of the females had viewed pornography at some point.

Further support for streaming Internet porn as unique stimulus:

Other slides providing support for streaming internet porn as a unique stimulus: slide 6, slide 7, slide 8, slide 18.

An excerpt from this 2016 peer-reviewed review of the literature I wrote with 7 US Navy doctors "Is Internet Pornography Causing Sexual Dysfunctions? A Review with Clinical Reports", which highlights several unique properties of streaming internet pornography:

3.2. Internet Pornography as Supernormal Stimulus

Arguably, the most important development in the field of problematic sexual behavior is the way in which the Internet is influencing and facilitating compulsive sexual behavior [73]. Unlimited high-definition sexual videos streaming via “tube sites” are now free and widely accessible, 24 h a day via computers, tablets and smartphones, and it has been suggested that Internet pornography constitutes a supernormal stimulus, an exaggerated imitation of something our brains evolved to pursue because of its evolutionary salience [74,75]. Sexually explicit material has been around for a long time, but (1) video pornography is significantly more sexually arousing than other forms of pornography [76, 77] or fantasy [78]; (2) novel sexual visuals have been shown to trigger greater arousal, faster ejaculation, and more semen and erection activity compared with familiar material, perhaps because attention to potential novel mates and arousal served reproductive fitness [75, 79, 80, 81, 82, 83, 84]; and (3) the ability to self-select material with ease makes Internet pornography more arousing than pre-selected collections [79]. A pornography user can maintain or heighten sexual arousal by instantly clicking to a novel scene, new video or never encountered genre. A 2015 study assessing Internet pornography’s effects on delay discounting (choosing immediate gratification over delayed rewards of greater value) states, “The constant novelty and primacy of sexual stimuli as particularly strong natural rewards make internet pornography a unique activator of the brain’s reward system. ... It is therefore important to treat pornography as a unique stimulus in reward, impulsivity, and addiction studies” [75] (pp. 1, 10).

Novelty registers as salient, enhances reward value, and has lasting effects on motivation, learning and memory [85]. Like sexual motivation and the rewarding properties of sexual interaction, novelty is compelling because it triggers bursts of dopamine in regions of the brain strongly associated with reward and goal-directed behavior [66]. While compulsive Internet pornography users show stronger preference for novel sexual images than healthy controls, their dACC (dorsal anterior cingulate cortex) also shows more rapid habituation to images than healthy controls [86], fueling the search for more novel sexual images. As co-author Voon explained about her team’s 2015 study on novelty and habituation in compulsive Internet pornography users, “The seemingly endless supply of novel sexual images available online [can feed an] addiction, making it more and more difficult to escape” [87]. Mesolimbic dopamine activity can also be enhanced by additional properties often associated with Internet pornography use such as, violation of expectations, anticipation of reward, and the act of seeking/surfing (as for Internet pornography) [88, 89, 90, 91, 92, 93]. Anxiety, which has been shown to increase sexual arousal [89, 94], may also accompany Internet pornography use. In short, Internet pornography offers all of these qualities, which register as salient, stimulate dopamine bursts, and enhance sexual arousal.

Excerpts from a 2017 peer-reviewed review of the literature, Pornography, Pleasure, and Sexuality: Towards a Hedonic Reinforcement Model of Sexually Explicit Internet Media Use, which describes unique properties of streaming internet pornography.

Hedonic Reinforcement:

In the second point of the model, we posit that IP serves as a particularly potent reinforcement of hedonic sexual motives. Whereas sexual activity of any kind is likely rewarding on some level, IP presents the potential for a combination of specific, easily obtainable, continually novel, and virtually immediate rewards in a manner that is uniquely and intensely rewarding (e.g., Gola et al., 2016). Many popular, non-empirical works have suggested as much (e.g., Foubert, 2016; Wilson, 2014; Struthers, 2009). Additionally, some limited reviews have considered the possibility that IP represents an abnormally rewarding stimulus (e.g., Barrett, 2010; Hilton, 2013; Grinde, 2002) in the context of human evolution. However, to date, there has been no systematic review examining the possibility that pornography represents an especially powerful hedonic reward. In the following sections, we review evidence for this second step.

Summary of Unique Reinforcement:

Collectively, the reviewed literature suggests that IP is indeed a unique and potent reward for hedonic sexual motives. IP is an easily accessible form of sexual stimuli that requires little effort or time on the part of the consumer. In contrast with partnered sexual activity, or even non-internet-based sexually explicit media, IP is a low cost and functionally instantaneous reward. Not surprisingly, the low-cost nature of IP (i.e., low financial and energy expenditures) is often reported as a motivating factor for consumption. IP is also highly customizable to the user’s preferences, fantasies, and desires. The functionally unlimited variety of IP available allows users to discover, explore, and cultivate nuanced and highly specific sexual desires. As hedonic sexual motives are the primary driving factor in IPU, the customizable and continually novel nature of IP represents a unique and potent reward for these motives.

A neurological paper published after the TEDx talk: Pornography addiction – a supranormal stimulus considered in the context of neuroplasticity (2013). An excerpt:

While pathological gambling (PG) and obesity have received greater attention in functional and behavioral studies, evidence increasingly supports the description of CSBs [compulsive sexual behavior] as an addiction. This evidence is multifaceted and is based on an evolving understanding of the role of the neuronal receptor in addiction-related neuroplasticity, supported by the historical behavioral perspective. This addictive effect may be amplified by the accelerated novelty and the ‘supranormal stimulus’ (a phrase coined by Nikolaas Tinbergen) factor afforded by Internet pornography.

Trading Later Rewards for Current Pleasure: Pornography Consumption and Delay Discounting (2015) – Researchers divided subjects into 2 groups: Half tried to abstain from their favorite food; half tried to abstain from internet porn. The subjects who tried to abstain from porn experienced significant changes: they scored better on their ability to delay gratification. The researchers said:

"The finding suggests that Internet pornography is a sexual reward that contributes to delay discounting differently than other natural rewards. It is therefore important to treat pornography as a unique stimulus in reward, impulsivity, and addiction studies and to apply this accordingly in individual as well as relational treatment.”


SLIDE 4

As you can see from this Australian experiment, it's not mere nudity, but novelty that sends arousal skyrocketing. Subjects watched 22 porn displays. See that spike? That’s where researchers switched to porn the guys hadn't seen before. The result: subjects' brains and boners fired up.

ORIGINAL SUPPORT:

The study presented in slide #4: Allocation of attentional resources during habituation and dishabituation of male sexual arousal (1999). Additional human studies aligning with Australian study's findings:

  1. Changes in the Magnitude of the Eyeblink Startle Response During Habituation of Sexual Arousal (2000) - "Repeated display of the film segment resulted in a progressive decrease in sexual arousal. Replacing the familiar stimulus by a novel erotic stimulus increased in sexual arousal and absorption and reduced startle (novelty effect)."
  2. Habituation and Dishabituation of Male Sexual Arousal (1993) - "Sixteen men were tested under conditions where they viewed the same segment of erotic film on many occasions... Increases in sexual arousal when novel erotic stimulation was introduced following habituation"
  3. Habituation and dishabituation of male sexual arousal - "increases in sexual arousal when novel erotic stimulation was introduced following habituation"
  4. Changes in erectile response to repeated audiovisual sexual stimulation (1998) - "Rigidity on the third day was significantly decreased compared to that on the first day in both patients with psychogenic impotence and normal controls"...
  5. The Long Term Habituation of Sexual Arousal in The Human Male (1991) - "in the constant stimulus conditions the criteria for long-term habituation generally were met. By contrast, responses to variable stimuli remained consistently high."
  6. Focusing “Hot” or Focusing “Cool”: Attentional Mechanisms in Sexual Arousal in Men and Women (2011) - "sexual feelings diminished during repeated erotic stimulation, and increased with the introduction of novel stimulation, indicating habituation and novelty effects. Contrary to the expectations, the hot attentional focus did not preclude habituation of sexual arousal."
  7. The Habituation of Sexual Arousal (1985) - "These results were interpreted as supporting the notions that sexual arousal to erotic stimuli decreases with repeated stimulus presentations"
  8. Repeated exposure to sexually explicit stimuli: novelty, sex, and sexual attitudes (1986) "Analyses showed that negative affect significantly increased with film repetition and returned to original levels with the introduction of novelty....with males becoming more aroused and concerned by novelty consisting of different actors, and females becoming more aroused and concerned by the same actors performing different acts."

UPDATED SUPPORT:

1) Habituation of sexual responses in men and women: a test of the preparation hypothesis of women's genital responses (2013) - Excerpt:

Men and women displayed very similar patterns of genital responses, consistent with habituation and novelty effects. Effects of habituation and novelty were eliminated once subjective reports of attention were covaried.

2) A review of the literature on animals and humans (includes studies employing pornography): Hormones and the Coolidge effect. Molecular and Cellular Endocrinology (2017) - An excerpt:

In both, males and females, there is a decline of sexual arousal after repeated exposition to the same sexual stimulus. This effect seems to be general to the whole range of species studied, including humans, although the results in women have to be further explored. Sexual novelty increases motivational aspects of sexual behavior in males, evidenced by the Coolidge effect.... The molecular mechanisms underlying sexual satiety are poorly understood; recent experimental data in rats suggest that dopamine may play a similar role in both sexes


SLIDE 5

Why all the excitement? (A slide with sheep.) Mother nature likes to keep a male fertilizing willing females - as long as any new ones are around. A ram needs more and more time to mate with the same old ewe. But if you keep switching females, he can get the job done in two minutes – and keep going until he is utterly exhausted. This is known as the "Coolidge effect.“ Without the Coolidge effect…there would be no Internet porn.

ORIGINAL SUPPORT:

1) Glenn Wilson on the Coolidge Effect, and 2) Copulatory behaviour of the ram, Ovis aries. I. A normative study (1969).

The previous two slides provided the bulk of the support for the concepts of habituation to the same old stimulus and the introduction of sexual novelty increasing sexual arousal and motivation. A few more studies considered when producing this slide:

UPDATED SUPPORT:

Further evidence of the "Coolidge Effect" in humans now exists.

1) Specific to pornography - men ejaculate more motile sperm and they do it more quickly when they view a novel porn star: Men Ejaculate Larger Volumes of Semen, More Motile Sperm, and More Quickly when Exposed to Images of Novel Women (2015)

2) Role of Partner Novelty in Sexual Functioning: A Review (2014). An excerpt:

This review investigates whether sexual desire and arousal decline in response to partner familiarity, increase in response to partner novelty, and show differential responding in men and women.... The current literature best supports the predictions made by sexual strategies theory in that sexual functioning has evolved to promote short-term mating. Sexual arousal and desire appear to decrease in response to partner familiarity and increase in response to partner novelty in men and women. Evidence to date suggests this effect may be greater in men. 

3) Another recent review of the literature on animals and humans (includes studies employing pornography): Hormones and the Coolidge effect. Molecular and Cellular Endocrinology (2017). An excerpt:

In both, males and females, there is a decline of sexual arousal after repeated exposition to the same sexual stimulus. This effect seems to be general to the whole range of species studied, including humans, although the results in women have to be further explored. Sexual novelty increases motivational aspects of sexual behavior in males, evidenced by the Coolidge effect.... The molecular mechanisms underlying sexual satiety are poorly understood; recent experimental data in rats suggest that dopamine may play a similar role in both sexes


SLIDE 6

This old mammalian program perceives each novel "mate" on a guy's screen as an opportunity to pass on his genes. To keep a guy fertilizing the screen, his brain releases the "go get it!" neurochemical dopamine for each new image or scene. Eventually the ram will tire, but as long as a guy can keep clicking, he can keep on going – and so will his dopamine. With Internet porn, a guy can see more hot babes in ten minutes than his hunter-gatherer ancestors could in several lifetimes. The problem is we have a hunter-gatherer brain.

ORIGINAL SUPPORT:

The previous 2 slides contain supporting materials. It's well established that both sexual arousal and novelty increase mesolimbic dopamine, and that exogenous dopamine can increase sexual arousal and motivation. A few supporting reviews of the literature:

UPDATED SUPPORT:

1) An excerpt from a peer-reviewed review of the literature that explains the role of dopamine in sexual arousal, motivation, and erections - Is Internet Pornography Causing Sexual Dysfunctions? A Review with Clinical Reports (2016):

3.1. Male Sexual Response in the Brain

While male sexual response is complex, several key brain regions are critical for achieving and maintaining erections [61]. Hypothalamic nuclei play an important role in regulating sexual behavior and erections by acting as an integration center for brain and peripheral input [62]. The hypothalamic nuclei that facilitate erections receive pro-erectile input from the mesolimbic dopamine pathway, which comprises the ventral tegmental area (VTA) and the nucleus accumbens (NAc) [62]. The VTA-NAc circuit is a key detector of rewarding stimuli, and forms the core of a broader, more complex set of integrated circuits commonly called the “reward system” [63]. An individual’s response to natural rewards, such as sex, is largely regulated by the mesolimbic dopamine pathway, which receives excitatory and inhibitory input from other limbic structures and the prefrontal cortex [64]. Erections are dependent upon activation of dopaminergic neurons in VTA and dopamine receptors in the NAc [65, 66]. Excitatory glutamate inputs from other limbic structures (amygdala, hippocampus) and the prefrontal cortex facilitate dopaminergic activity in the VTA and NAc [62]. Reward responsive dopamine neurons also project into the dorsal striatum, a region activated during sexual arousal and penile tumescence [67]. Dopamine agonists, such as apomorphine, have been shown to induce erection in men with both normal and impaired erectile function [68]. Thus, dopamine signaling in the reward system and hypothalamus plays a central role in sexual arousal, sexual motivation and penile erections [65, 66, 69].

We propose that chronic Internet pornography use resulted in erectile dysfunction and delayed ejaculation in our servicemen reported above. We hypothesize an etiology arising in part from Internet pornography-induced alterations in the circuits governing sexual desire and penile erections. Both hyper-reactivity to Internet pornography cues via glutamate inputs and downregulation of the reward system’s response to normal rewards may be involved. These two brain changes are consistent with chronic overconsumption of both natural rewards and drugs of abuse, and are mediated by dopamine surges in the reward system [70, 71, 72].

2) This 2017 review of the literature, Pornography, Pleasure, and Sexuality: Towards a Hedonic Reinforcement Model of Sexually Explicit Internet Media Use, supports the thesis that endless novelty and instant customizability (novel genres) drives internet porn use:

Novelty and Customizable Nature of IP

Another facet of highly rewarding stimuli is the alignment of the stimuli with a person’s preferences. Within the desire and motivation literature, there is often a distinction made between “liking” or “wanting” something (Berridge, 1996; Voon et al., 2014). Liking refers to the pleasure derived from a stimulus or the degree to which a stimulus satisfies a hedonic urge (Berridge, 1996). In contrast, wanting refers to the rewarding value of a stimulus or the degree to which a stimulus satisfies a biological or appetitive drive (Berridge, 1996), or in the case of addiction, a dependence on a substance. Although such a distinction has been most often studied in regards to food (e.g., Berridge, 2009; Finlayson, King, & Blundell, 2007), similar understandings of liking vs. wanting have been proposed for alcohol use (Hobbs, Remington, & Glautier, 2005) other substances (e.g., cocaine, Goldstein et al., 2008), and also for compulsive use of pornography (Voon et al., 2014). Oftentimes, the rewards thought to be most powerful are those that involve both liking and wanting. Stimuli that satisfy a drive (e.g., hunger) in a way that also satisfies the person’s individual, specific preferences (e.g., specific flavor combinations), are likely to be considered more rewarding than stimuli that meet only one such criteria (Berridge & Robinson, 2003). A similar understanding may also be applied to IPU.

Content analyses of online forums note that pornography preferences are often the subject of entire online-communities, with significant effort being devoted to the categorization and accurate indexing of pornographic materials according to users’ preferences (Smith, 2015). This is accomplished both on non-pornographic web-sites (e.g., reddit.com, Smith, 2015), as well as more popular IP websites (Fesnak, 2016; Hald & Štulhofer, 2015; Mazieres, Trachman, Cointet, Coulmont, & Prieur, 2014; Vincent, 2016). By design alone, these categorizations represent an important way in which IP is customized to user preferences. IP categories allow users to immerse themselves in content that specifically matches their sexual desires, giving them a custom reward for a specific sexual desire, and it allows individuals to do this with limited social effort or risk.

Several works in the social sciences (e.g., Cusack & Waranious, 2012; Vannier, Currie, & O’Sullivan, 2014) as well as the humanities (e.g., Strager, 2003) have expounded upon the customizable nature of IPU. The immense variety of content in IP allows users to explore and encounter a functionally infinite amount of novel and unique materials (Ogas & Goddam, 2013; Barratt, 2014; Tyson, Elkhatib, Sastry, & Uhligh, 2013), which is particularly relevant given humans’ preference for and responsiveness to novel sexual partners (Morton & Gorzalka, 2015). Various factors, such as current events and individual differences, predict the types of content that are searched for by IPU consumers (e.g., Markey & Markey, 2010, 2011). Furthermore, many content analyses have found that a large variety of specific fantasies, fetishes, and sexual desires are well-represented in IP (Downing, Scrimshaw, Antebi, & Siegel, 2014; Glasscock, 2005; Michael & Plaza, 1997; Vannier et al., 2014; Sun, Bridges, Wosnitzer, Scharrer, & Liberman, 2008; Zhou & Paul, 2016). While this may allow users the freedom to explore new aspects of their sexual curiosities and fantasies (Ley, 2016), it also presents users with the option to focus their IPU on highly specific sexual stimuli that both satisfy their sexual drive (i.e., wanting, Svedin, Akerman, & Priebe, 2011) and their sexual preferences (i.e., liking, Half & Štulhofer, 2015). Essentially, the variety of content available in IP allows for highly custom rewards for hedonic sexual desires.

Prior theoretical works (e.g., Keilty, 2012; Patterson, 2004), have expounded upon the tendency of some IP consumers to engage in prolonged searches for “perfect” or highly-stimulating images or videos that are suitable for fulfilling a sexual fantasy. Unstructured, qualitative interviews have found similar themes among IP consumers, again suggesting that customization and control are important aspects of IP’s rewarding nature (Philaretou et al., 2005).

Moving beyond clear theoretical arguments, there is also empirical evidence to suggest that IPU is highly customized to the users’ preferences, representing a unique and potentially potent reward for hedonic desires. In two studies of young adult men in the U.S. (Study 1 N=103, Study 2 N=88), IPU (yes/no to current use) was found to be moderately-to-strongly associated with the presence of atypical sexual fantasies (e.g., fetishism, frotteurism, exhibitionism; Williams, Cooper, Howell, Yullie, & Paulhus, 2009). Similarly, in a cross-sectional study of middle-aged and older (40+ years old) German men (N=367), IPU was again associated with paraphilic sexual desires and arousal (Ahlers et al., 2011). In both examples, causality is not specified, given their cross-sectional natures. However, given that there is no conclusive evidence suggesting that pornography use may lead to paraphilia (for a review, see Fisher, Kohut, Di Gioacchino, & Fedoroff, 2013), these studies may be understood as evidence that IPU is positively associated with highly specific preferences.

Similarly, in a study of Croatian adults (N=2,337; 43% men; 64-65.7% heterosexual), a wide variety of pornography preferences were identified (Hald & Štulhofer, 2015). More specifically, among 27 types of IP, Hald and Štulhofer found that participants often endorsed highly specific preferences that varied by gender and sexual orientation. Across these groups and within individuals, there were noted differences in preferences for the focus of IP (e.g., individual performer vs. couple vs. group), the physical features of the performers (both male and female), and the types of sexual acts being displayed. Collectively, these findings provide further evidence for the idea that IPU is often tailored to the consumer’s specific preferences, presenting the opportunity for a unique and powerful reward.


SLIDE 7

Internet porn registers as a genetic bonanza - so, a heavy porn user’s brain carefully wires his sexual response to everything associated with his porn viewing. Being alone, Voyeurism, Clicking, Searching, Multiple tabs, Constant novelty, Shock or surprise. As one young guy asked: "Are we the first generation to masturbate left-handed?"

ORIGINAL SUPPORT:

The claim is that a chronic porn user can condition his sexual arousal to everything associated with his porn use, rather than to partnered sex. "Wiring" one's sexual arousal to internet porn is most evident in men developing porn-induced sexual problems. See the "Updated Support" section of slide 32 for a large body of evidence supporting this assertion.

Much original support came from anecdotal evidence: (1) porn users describing escalation of porn use into "shocking" genres or porn that induced anxiety; (2) development of porn-induced sexual problems where men could only become aroused by porn; (3) needing constant visual novelty to stay aroused; (4) searching for just the right visual to finish the session. These observations aligned with psychiatrist Norman Doidge's 2007 bestseller "The Brain That Changes Itself", which also claimed that internet porn use can alter sexual scripts. Excerpts in support of slide 7:

During the mid- to late 1990s, when the internet was growing rapidly and pornography was exploding on it, I treated or assessed a number of men who all had essentially the same story. They reported increasing difficulty in being turned on by their actual sexual partners, spouses, or girlfriends, though they still considered them objectively attractive. The content of what patients found exciting changed as the web sites introduced themes and scripts that altered their brains without their awareness. Because plasticity is competitive, the brain maps for new, exciting images increased at the expense of what had previously attracted them. Today, young men who surf porn are tremendously fearful of impotence, or "erectile dysfunction" as it is euphemistically called. The misleading term implies that these men have a problem in their penises, but the problem is in their heads. It rarely occurs to them that there may be a relationship between the pornography they are consuming and their impotence.

A 2007 study by the Kinsey Institute supports the thesis that chronic porn use can lead to the user "needing" the porn to become sexually aroused (The Dual Control Model - The Role Of Sexual Inhibition & Excitation In Sexual Arousal And Behavior). In an experiment employing video porn, 50% of the young men couldn't become aroused or achieve erections with porn (average age was 29). The shocked researchers discovered that the men's erectile dysfunction was,

"related to high levels of exposure to and experience with sexually explicit materials."

The men experiencing erectile dysfunction had spent a considerable amount of time in bars and bathhouses where porn was "omnipresent," and "continuously playing." The researchers stated:

"Conversations with the subjects reinforced our idea that in some of them a high exposure to erotica seemed to have resulted in a lower responsivity to "vanilla sex" erotica and an increased need for novelty and variation, in some cases combined with a need for very specific types of stimuli in order to get aroused."

Shifting Preferences In Pornography Consumption (1986) - Six weeks of exposure to nonviolent pornography resulted in subjects having little interest in vanilla porn, electing to almost exclusively watch "uncommon pornography" (bondage, sadomasochism, bestiality). An excerpt:

Male and female students and nonstudents were exposed to one hour of common, nonviolent pornography or to sexually and aggressively innocuous materials in each of six consecutive weeks. Two weeks after this treatment, they were provided with an opportunity to watch videotapes in a private situation. G-rated, R-rated, and X-rated programs were available. Subjects with considerable prior exposure to common, nonviolent pornography showed little interest in common, nonviolent pornography, electing to watch uncommon pornography (bondage, sadomasochism, bestiality) instead. Male nonstudents with prior exposure to common, nonviolent pornography consumed uncommon pornography almost exclusively. Male students exhibited the same pattern, although somewhat less extreme. This consumption preference was also in evidence in females, but was far less pronounced, especially among female students.

Use of pornography in a random sample of Norwegian heterosexual couples (2009) - Porn use correlated with more sexual dysfunctions in the men and negative self-perception in the women. The couples who did not use porn had no sexual dysfunctions. A few excerpts from the study:

In couples where only one partner used pornography, we found more problems related to arousal (male) and negative (female) self-perception.

In those couples where one partner used pornography there was a permissive erotic climate. At the same time, these couples seemed to have more dysfunctions.

The couples who did not use pornography... may be considered more traditional in relation to the theory of sexual scripts. At the same time, they did not seem to have any dysfunctions.

UPDATED SUPPORT:

First, a few excerpts from a review of the literature on sexual conditioning, Who, what, where, when (and maybe even why)? How the experience of sexual reward connects sexual desire, preference, and performance (2012):

Although sexual behavior is controlled by hormonal and neurochemical actions in the brain, sexual experience induces a degree of plasticity that allows animals to form instrumental and Pavlovian associations that predict sexual outcomes, thereby directing the strength of sexual responding. This review describes how experience with sexual reward strengthens the development of sexual behavior and induces sexually-conditioned place and partner preferences in rats… Thus, a critical period exists during an individual's early sexual experience that creates a "love map" or Gestalt of features, movements, feelings, and interpersonal interactions associated with sexual reward.

We propose that the development of sexual ‘‘Gestalts’’ and sexual ‘‘scripts’’ (from the standpoint of both movements and language) are affected strongly by early formative experiences with sexual arousal and reward that feed forward to create desire for distal, proximal, and interactive features that predict the reward state. This occurs to some extent uniquely in the development of everyone’s sexual preferences, although some commonalities may be easy to detect in terms of species-specific behavior or stimulation patterns, or as distal features of ‘‘attractiveness’’, such as the gender of the desired individual, race, age, body type, hair or eye color, facial features, and even the intergenerational styles of personal presentation (e.g., differences in facial structure, hair style, presence or absence of pubic, body, and facial hair of pin-ups from the first half of the twentieth century relative to the second half; see Gabor, 1973)   

Building on the concept of critical widows of development (early adolescence), the following paper found that early sexual experience can influence an individual's sexual trajectory (i.e. porn addiction or sex addiction): Human Sexual Development is Subject to Critical Period Learning: Implications for Sexual Addiction, Sexual Therapy, and for Child Rearing (2014) - Excerpts:

To our knowledge, ours is the first study to directly investigate whether learning to function sexually is subject to critical period learning in humans. The results of our statistical analyses were highly consistent in both men and women with a critical period learning effect because the scores on subscales measuring both adult interest in sex (Hypersexuality Subscale) and the likelihood of engaging in risky sexual behaviors (Risky Sexual Behavior Subscale) tended to be increased if participant’s first experience with partner sex had occurred early in life and if they had started masturbating early in life. Our findings, with regard to masturbation, were supported by other studies on the adult effects of early masturbatory experiences (e.g., Brody et al., 2013; Carvalheira & Leal, 2013; Das, 2007; Hogarth & Ingham, 2009). The age that our participants reported having first masturbated had the largest effect size as a predictor of their adult interest in sex as measured by the Hypersexuality Subscale, and the earliest age participants reported having engaged in sexual behavior of any kind with a partner had the second largest effect size. Participants who began these behaviors before 13 years of age had the highest interest in sex as adults.

The results of our study provided a new theoretical and developmental basis for both origins of sexual addiction on the one hand and hypoactive sexual desire on the other hand. The higher interest in sex observed in those who had early experience with partner sex and masturbation can be explained by the combined action of Pavlovian conditioning, operant conditioning, and critical period learning initiated by early experience with partner sex with or without the synergistic effect of an early experience with masturbation (Beard et al., 2013; O’Keefe et al., 2014; also see Hoffmann, 2012 and Pfaus et al., 2012 for a reviews of conditioning theories and experimental data). On the other hand, a low interest in sex appeared to be the result when both such experiences were lacking. Sexual imprinting would provide a third etiological explanation. Sexual imprinting is the kind of critical period learning (Desmarais et al., 2012; Fox & Rutter, 2010; Fox et al., 2010; Uylings, 2006) initially used to explain the observation that birds raised by foster-parents of other species preferred mates of the foster-parent’s species (for review see Irwin & Price, 1999). In humans, sexual imprinting has been invoked to explain sexual preferences for partners who resemble their opposite sex parents (Bereczkei, Gyuris, & Weisfeld, 2004; Nojo, Tamura, & Uhara, 2012), some men’s preferences for lactating or pregnant women (Enquist, Aronsson, Stefano, Jansson, & Jannini, 2011), and willingness to accept sexual partners who smoke (Aronsson, Lind, Ghirlanda, & Enquist, 2011). It is highly likely that many other kinds of learning are involved in producing the phenomenology described in our article, but cataloging all of the types of learning involved is a project beyond the scope of the present research.

Excerpts from Is Internet Pornography Causing Sexual Dysfunctions? A Review with Clinical Reports (2016) underscore how internet porn use conditions the sexual response to variables not seen in real life sexual encounters. From the abstract:

This review also considers evidence that Internet pornography’s unique properties (limitless novelty, potential for easy escalation to more extreme material, video format, etc.) may be potent enough to condition sexual arousal to aspects of Internet pornography use that do not readily transition to real-life partners, such that sex with desired partners may not register as meeting expectations and arousal declines.

From the discussion section:

3.4.3. Internet Pornography and Sexual Conditioning

Given that our servicemen reported that they experienced erections and arousal with Internet pornography, but not without it, research is needed to rule out inadvertent sexual conditioning as a contributing factor to today’s rising rates of sexual performance problems and low sexual desire in men under 40. Prause and Pfaus have hypothesized that sexual arousal may become conditioned to aspects of Internet pornography use that do not readily transition to real-life partner situations. “It is conceivable that experiencing the majority of sexual arousal within the context of VSS [visual sexual stimuli] may result in a diminished erectile response during partnered sexual interactions...When high stimulation expectations are not met, partnered sexual stimulation is ineffective” [50]. Such inadvertent sexual conditioning is consistent with the incentive-salience model. Several lines of research implicate increased mesolimbic dopamine in sensitization to both drugs of abuse and sexual reward [100,103]. Acting through dopamine D1 receptors, both sexual experience and psychostimulant exposure induce many of the same long-lasting neuroplastic changes in the NAc critical for enhanced wanting of both rewards [103].

Today’s Internet pornography user can maintain high levels of sexual arousal, and concomitant elevated dopamine, for extended periods due to unlimited novel content. High dopamine states have been implicated in conditioning sexual behavior in unexpected ways in both animal models [176, 177] and humans. In humans, when Parkinson’s patients were prescribed dopamine agonists, some reported uncharacteristic compulsive pornography use and demonstrated greater neural activity to sexual picture cues, correlating with enhanced sexual desire [178]. Two recent fMRI studies reported that subjects with compulsive sexual behaviors are more prone to establish conditioned associations between formally neutral cues and explicit sexual stimuli than controls [86, 121]. With repeated Internet pornography exposure, “wanting” may increase for Internet pornography’s expected novelty and variety, elements difficult to sustain during partnered sex. In line with the hypothesis that Internet pornography use can condition sexual expectations, Seok and Sohn found that compared to controls hypersexuals had greater DLPFC activation to sexual cues, yet less DLPFC activation to non-sexual stimuli [120]. It also appears that Internet pornography use can condition the user to expect or “want” novelty. Banca et al. reported that subjects with compulsive sexual behaviors had greater preference for novel sexual images and showed greater habituation in the dorsal anterior cingulate cortex to repeated viewing of the same sexual images [86]. In some users, a preference for novelty arises from the need to overcome declining libido and erectile function, which may, in turn, lead to new conditioned pornographic tastes [27].

When a user has conditioned his sexual arousal to Internet pornography, sex with desired real partners may register as “not meeting expectations” (negative reward prediction) resulting in a corresponding decline in dopamine. Combined with the inability to click to more stimulation, this unmet prediction may reinforce an impression that partnered sex is less salient than Internet pornography use. Internet pornography also offers a voyeur's perspective generally not available throughout partnered sex. It is possible that if a susceptible Internet pornography user reinforces the association between arousal and watching other people have sex on screens while he is highly aroused, his association between arousal and real-life partnered sexual encounters may weaken.

Research on conditioning of sexual response in humans is limited, but shows that sexual arousal is conditionable [179, 180, 181], and particularly prior to adulthood [182]. In men, arousal can be conditioned to particular films [183], as well as to images [184]. Sexual performance and attraction in male (non-human) animals can be conditioned to an array of stimuli that are not typically sexually salient for them, including fruit/nut scents, aversive scents, such as cadaverine, same-sex partners, and the wearing of rodent jackets [177, 185, 186, 187]. For example, rats that had learned sex with a jacket did not perform normally without their jackets [187].

In line with these conditioning studies, the younger the age at which men first began regular use of Internet pornography, and the greater their preference for it over partnered sex, the less enjoyment they report from partnered sex, and the higher their current Internet pornography use [37]. Similarly, men reporting increased consumption of bareback anal pornography (in which actors do not wear condoms) and its consumption at an earlier age, engage in more unprotected anal sex themselves [188, 189]. Early consumption of pornography may also be associated with conditioning tastes to more extreme stimulation [99,190].

A review by Pfaus points to early conditioning as critical for sexual arousal templates: “It is becoming increasingly clear that there is a critical period of sexual behavior development that forms around an individual’s first experiences with sexual arousal and desire, masturbation, orgasm, and sexual intercourse itself” [191] (p. 32). The suggestion of a critical developmental period is consistent with the report of Voon et al. that younger compulsive Internet pornography users showed greater activity in the ventral striatum in response to explicit videos [31]. The ventral striatum is the primary region involved in sensitization to natural and drug reward [103]. Voon et al. also reported that compulsive Internet pornography subjects first viewed Internet pornography much earlier (mean age 13.9) than healthy volunteers (mean age 17.2) [31]. A 2014 study found that nearly half of college-age men now report they were exposed to Internet pornography prior to age 13, as compared with only 14% in 2008 [37]. Could increased Internet pornography use during a critical developmental phase increase the risk of Internet pornography-related problems? Might it help explain the 2015 finding that 16% of young Italian men who used Internet pornography more than once a week reported low sexual desire, compared with 0% in non-consumers [29]? Our first serviceman was only 20 and had been using Internet pornography since he gained access to high-speed Internet.

Males can successfully condition their sexual response in the laboratory with instructional feedback, but without further reinforcement, such laboratory-induced conditioning disappears in later trials [176]. This inherent neuroplasticity may suggest how two of our servicemen restored attraction and sexual performance with partners after abandoning a sex toy and/or cutting back on Internet pornography. Decreasing or extinguishing conditioned responses to artificial stimuli potentially restored attraction and sexual performance with partners.

Excerpts from a 2017 review of the literature (Pornography, Pleasure, and Sexuality: Towards a Hedonic Reinforcement Model of Sexually Explicit Internet Media Use) describe a different set of criteria to explain how internet pornography use shapes sexual expectations (i.e. less desire for partnered sex, less sexual satisfaction, poorer relationships):

Summary and Implications of the Present Model

The present work represents a novel organization of the research literature related to IPU and the proposition of a new theoretical model. In proposing this model and reviewing the literature, we have attempted to demonstrate how IPU may be related to specific aspects of sexual motivation. We have shown that IPU is primarily driven by hedonic sexual motives, that it is uniquely reinforcing of those motives, and that it is likely contributing to a strengthening of those motives in individual sexual motivation. Several implications flow naturally from our model, which we review below.

Social Sexual Orientation

A clear implication of the model is that IPU might ultimately be associated with a decreased social or relational orientation, particularly in the context of sexual relationships and intimacy. Early empirical research on IP showed that it might be associated with infidelity, reduced commitment, and weakened partner bonds (Young, Griffin-Shelley, Cooper, O’mara, & Buchanan, 2000), and more recent research has demonstrated that pornography may impact romantic partners in various ways (Syzmanski, Feltman, & Dunn, 2015; Tylka & Kroon Van Diest, 2015). Furthermore, a large percentage of both men and women report that IPU is currently or will likely be a part of their romantic relationships, either being used by one or by both partners (Carroll, Busby, Willoughby, & Brown, 2016; Olmstead, Negash, Pasley, & Fincham, 2013).  Historically, pornography has been linked to diminished love for and attraction to a partner (Kenrick, Gutierres, and Goldberg, 1989).

There is indeed evidence that IPU is associated with weakened commitment to a romantic partner (Lambert et al., 2012). Across five studies, there was consistent evidence for the notion that IPU is broadly predictive of weakened commitment and fidelity to one’s romantic partner. In cross-sectional study data (Lambert et al., 2012; Study 1), participants that reported greater IPU also reported lower levels of commitment to the partner. Moving forward (Study 2), third person observers accurately rated IP consumers as demonstrating less commitment to their romantic partners in social interactions. These findings were further supported by experimental data (Study 3) in which those who refrained from IPU for a period of time were likely to report greater commitment to their romantic partners than IP consumers. Finally, using behavioral observation, it was found that IPU was associated with greater flirtatiousness in online conversation (Study 4) and with a greater likelihood to commit infidelity over time (Study 5). Collectively, these findings paint a consistent picture in which IPU is associated with reduced relational commitment.

There is also some evidence that IPU is associated with greater openness toward extramarital sexual engagements, which may be seen as a proxy for weakened relational commitment. Specifically, in a previously reviewed nationally representative sample of men in the U.S. (General Social Survey from 2000 & 2002; Wright, 2012b), IPU was associated with greater openness to a variety of uncommitted sexual behaviors, including extramarital sexual engagements. Additionally, in analyses of women from the same sample (General Social Survey data from 2000 & 2002; Wright, 2013b), IPU was associated with more positive attitudes toward extramarital sex for women who were less educated and less religious.

Links between pornography use and diminished relational orientation or commitment are also evident longitudinally. In at least one longitudinal study, there were associations between IPU and extra-dyadic behaviors (Maddox et al., 2013). Specifically, among a large sample of unmarried heterosexuals in relationships (N=993), self-reported IPU with a partner was predictive of greater likelihood of extra dyadic behaviors over a 20-month time period, suggesting that it may play a causal role in leading to diminished sexual commitment. Furthermore, these results are supported by analyses of the Portraits of American Life study—a nationally representative sample of American adults—which found that pornography use was associated with reduced marital quality over time (Perry, 2016, 2017), and with analyses of General Social Survey data from 2006-2014 which found that individuals who initiated pornography use over the course of the panel study were at approximately twice the risk of divorce over the study’s 8 year time period (Perry & Schleifer, 2017).

In addition to nationally representative samples, experimental methods have also found that IPU is associated with more positive attitudes toward extra-dyadic behavior. Specifically, in a sample of undergraduates in monogamous committed relationships (Gwinn, Lambert, Fincham, & Maner, 2013; Study 1; N=74, 36% men, Median Age=19), reflecting on IPU (e.g., writing a description of a pornographic video watched in the past 30 days) was associated with believing that one had higher quality relationship alternatives. In a follow-up study of undergraduates in committed monogamous relationships (Gwinn et al., 2013; Study 2; N=291, 18% men, Median Age=20), IPU was longitudinally associated with engaging in extra-dyadic behaviors, so that, IPU reported at baseline was predictive of extra-dyadic behavior 12 weeks later.

Collectively, results from cross-sectional, longitudinal, nationally-representative, and experimental studies support the conclusion that pornography use in general and IPU specifically are associated with reduced relational commitment and quality. These findings are also consistent with the contention of the present model, that IPU is associated with increases in self-focused hedonic sexual motivation, often at the expense of other-oriented or social sexual motivations.

Sexual Satisfaction

Another domain in which the present model may also have implications is sexual satisfaction. As hedonic sexual motives are often focused on obtaining sexual satisfaction, one would expect an increase in such motives to be associated with sexual satisfaction outcomes. However, given the immense number of factors that contribute to sexual satisfaction (e.g., relational intimacy, commitment, self-confidence, self-esteem), it also likely that these relationships between IPU and satisfaction will be complex. For some individuals, an increase in hedonic sexual motives may be associated with actual decreases in sexual satisfaction, as high levels of desire may be met with frustration, particularly if such increases are not met with increases in the satisfaction associated with partnered sexual activity (Santtila et al., 2007). Alternatively, if one were to start with low levels of hedonic sexual motivation, an increase in such motivation may be associated with greater sexual satisfaction as the individual becomes more focused on obtaining pleasure in a sexual encounter.

In contrast to many of the previously discussed domains related to IPU and motivations, in which research is still burgeoning, the relationships between IPU and sexual satisfaction have been extensively studied, with dozens of publications addressing the topic. Rather than exhaustively review the list of studies examining IPU and sexual satisfaction, the findings of these studies are summarized in Table 1.

In general, as indicated in Table 1, the relationships between IPU and personal sexual satisfaction are complex, but consistent with the supposition that IP may promote more hedonic sexual motivations, particularly as use increases. Among couples, there is limited support for the idea that IPU may enhance sexual satisfaction, but only when it is incorporated into partnered sexual activities. On an individual level, there is consistent evidence that IPU is predictive of lower sexual satisfaction in men, with both cross-sectional and longitudinal works pointing to the associations of such use with diminished satisfaction for men. Regarding women, scattered evidence suggests that IPU may enhance sexual satisfaction, have no effect on satisfaction, or diminish satisfaction over time. Despite these mixed findings, the conclusion of no significant effect of IPU on sexual satisfaction in women is the most common finding. These results have also been confirmed by a recent meta-analysis (Wright, Tokunaga, Kraus, & Klann, 2017). Reviewing 50 studies of pornography consumption and various satisfaction outcomes (e.g., life satisfaction, personal satisfaction, relational satisfaction, sexual satisfaction), this meta-analysis found that pornography consumption (not internet-specific) was consistently related to and predictive of lower interpersonal satisfaction variables, including sexual satisfaction, but for men only. No significant findings were found for women. Collectively, such mixed results preclude definitive conclusions about the role of IP in influencing satisfaction for women.

One of the most important findings of recent works examining IPU and sexual satisfaction is that there appears to be a curvilinear relationship between use and satisfaction, so that satisfaction decreases more sharply as IPU becomes more common (e.g., Wright, Steffen, & Sun, 2017; Wright, Brigdes, Sun, Ezzell, & Johnson, 2017). The details of these studies are reflected in Table 1. Given clear evidence across multiple international samples, it seems reasonable to accept the conclusion that as IPU increases to more than once per month, sexual satisfaction decreases. Furthermore, although these studies (Wright, Steffen, et al., 2017; Wright, Bridges et al., 2017) were cross-sectional, given the number of longitudinal studies (e.g., Peter & Valkenburg, 2009) linking IPU to lower sexual satisfaction, it is reasonable to infer that these associations are causal in nature. As IPU increases, interpersonal sexual satisfaction appears to decrease, which is consistent with the present model’s contention that IPU is associated with more hedonic and self-focused sexual motivation.

As of 2017 there 24 studies linking porn use/sex addiction to sexual problems and lower arousal to sexual stimuli. Wiring or conditioning one's sexual arousal to internet porn is also seen in escalation into new genres, or needing new and unusual genres to become aroused. Three studies have now asked porn users specifically about escalation into new genres or tolerance, confirming both (1, 2, 3). Employing various indirect methods, an additional 16 studies have reported findings consistent with habituation to "regular porn" or escalation into more extreme and unusual genres. The following studies, selected from the two lists, demonstrate porn users conditioning their arousal template to internet porn:

1) Is Internet Pornography Causing Sexual Dysfunctions? A Review with Clinical Reports (2016). This an extensive review of the literature related to porn-induced sexual problems include 3 clinical reports of servicemen who developed porn-induced sexual dysfunctions. Two of the three servicemen healed their sexual dysfunctions by eliminating porn use while the third man experienced little improvement as he was unable to abstain from porn use. Two of the three servicemen reported habituation to current porn and escalation of porn use. The first serviceman describes his habituation to "soft porn" followed by escalation into more graphic and fetish porn: 

A 20-year old active duty enlisted Caucasian serviceman presented with difficulties achieving orgasm during intercourse for the previous six months. It first happened while he was deployed overseas. He was masturbating for about an hour without an orgasm, and his penis went flaccid. His difficulties maintaining erection and achieving orgasm continued throughout his deployment. Since his return, he had not been able to ejaculate during intercourse with his fiancée. He could achieve an erection but could not orgasm, and after 10–15 min he would lose his erection, which was not the case prior to his having ED issues.

Patient endorsed masturbating frequently for “years”, and once or twice almost daily for the past couple of years. He endorsed viewing Internet pornography for stimulation. Since he gained access to high-speed Internet, he relied solely on Internet pornography. Initially, “soft porn”, where the content does not necessarily involve actual intercourse, “did the trick”. However, gradually he needed more graphic or fetish material to orgasm. He reported opening multiple videos simultaneously and watching the most stimulating parts.

The second serviceman describes increased porn use and escalation into more graphic porn. Soon thereafter sex with his wife “not as stimulating as before":

A 40-year old African American enlisted serviceman with 17 years of continuous active duty presented with difficulty achieving erections for the previous three months. He reported that when he attempted to have sexual intercourse with his wife, he had difficulty achieving an erection and difficulty maintaining it long enough to orgasm. Ever since their youngest child left for college, six months earlier, he had found himself masturbating more often due to increased privacy. He formerly masturbated every other week on average, but that increased to two to three times per week. He had always used Internet pornography, but the more often he used it, the longer it took to orgasm with his usual material. This led to him using more graphic material. Soon thereafter, sex with his wife was “not as stimulating” as before and at times he found his wife “not as attractive”. He denied ever having these issues earlier in the seven years of their marriage. He was having marital issues because his wife suspected he was having an affair, which he adamantly denied.

2) Unusual masturbatory practice as an etiological factor in the diagnosis and treatment of sexual dysfunction in young men (2014) – One of the 4 case studies in this paper reports on a man with porn-induced sexual problems (low libido, fetishes, anorgasmia). After 8 months the man reported increased sexual desire, successful sex and orgasm, and enjoying “good sexual practices. Excerpts from the paper:

"When asked about masturbatory practices, he reported that in the past he had been masturbating vigorously and rapidly while watching pornography since adolescence. The pornography originally consisted mainly of zoophilia, and bondage, domination, sadism, and masochism, but he eventually got habituated to these materials and needed more hardcore pornography scenes, including transgender sex, orgies, and violent sex. He used to buy illegal pornographic movies on violent sex acts and rape and visualized those scenes in his imagination to function sexually with women. He gradually lost his desire and his ability to fantasize and decreased his masturbation frequency."

In conjunction with weekly sessions with a sex therapist, the patient was instructed to avoid any exposure to sexually explicit material, including videos, newspapers, books, and internet pornography..... After 8 months, the patient reported experiencing successful orgasm and ejaculation. He renewed his relationship with that woman, and they gradually succeeded in enjoying good sexual practices.

3) How difficult is it to treat delayed ejaculation within a short-term psychosexual model? A case study comparison (2017) - A report on "composite cases" illustrating the causes and treatments for delayed ejaculation (anorgasmia). "Patient B" represented several young men treated by the therapist. Interestingly, the paper states that Patient B's "porn use had escalated into harder material", "as is often the case". The paper says that porn-related delayed ejaculation is not uncommon, and on the rise. The author calls for more research on porn's effects of sexual functioning. Patient B's delayed ejaculation was healed after 10 weeks of no porn. Excerpts:

The cases are composite cases taken from my work within the National Health Service in Croydon University Hospital, London. With the latter case (Patient B), it is important to note that the presentation reflects a number of young males who have been referred by their GPs with a similar diagnosis. Patient B is a 19-year-old who presented because he was unable to ejaculate via penetration. When he was 13, he was regularly accessing pornography sites either on his own through internet searches or via links that his friends sent him. He began masturbating every night while searching his phone for image…If he did not masturbate he was unable to sleep. The pornography he was using had escalated, as is often the case (see Hudson-Allez, 2010), into harder material (nothing illegal)…

Patient B was exposed to sexual imagery via pornography from the age of 12 and the pornography he was using had escalated to bondage and dominance by the age of 15.

We agreed that he would no longer use pornography to masturbate. This meant leaving his phone in a different room at night. We agreed that he would masturbate in a different way….

Patient B was able to achieve orgasm via penetration by the fifth session; the sessions are offered fortnightly in Croydon University Hospital so session five equates to approximately 10 weeks from consultation. He was happy and greatly relieved. In a three-month follow-up with Patient B, things were still going well.

Patient B is not an isolated case within the National Health Service (NHS) and in fact young men in general accessing psychosexual therapy, without their partners, speaks in itself to the stirrings of change.

4) Neural Correlates of Sexual Cue Reactivity in Individuals with and without Compulsive Sexual Behaviours (2014) - This fMRI study by Cambridge University found sensitization in porn addicts which mirrored sensitization in drug addicts. It also found that porn addicts fit the accepted addiction model of wanting "it" more, but not liking "it" more. The researchers also reported that 60% of subjects (average age: 25) had difficulty achieving erections/arousal with real partners as a result of using porn, yet could achieve erections with porn. From the study (CSB is compulsive sexual behaviours):

CSB subjects reported that as a result of excessive use of sexually explicit materials.....[they] experienced diminished libido or erectile function specifically in physical relationships with women (although not in relationship to the sexually explicit material)

Compared to healthy volunteers, CSB subjects had greater subjective sexual desire or wanting to explicit cues and had greater liking scores to erotic cues, thus demonstrating a dissociation between wanting and liking. CSB subjects also had greater impairments of sexual arousal and erectile difficulties in intimate relationships but not with sexually explicit materials highlighting that the enhanced desire scores were specific to the explicit cues and not generalized heightened sexual desire.

5) Online sexual activities: An exploratory study of problematic and non-problematic usage patterns in a sample of men (2016) - This Belgian study from a leading research university found problematic Internet porn use was associated with reduced erectile function and reduced overall sexual satisfaction. Yet problematic porn users experienced greater cravings (sensitization). The study reports escalation, as 49% of the men viewed porn that "was not previously interesting to them or that they considered disgusting." Excerpt:

Forty-nine percent mentioned at least sometimes searching for sexual content or being involved in OSAs that were not previously interesting to them or that they considered disgusting, and 61.7% reported that at least sometimes OSAs were associated with shame or guilty feelings.

This Belgian study also found problematic Internet porn use was associated with reduced erectile function and reduced overall sexual satisfaction. Yet problematic porn users experienced greater cravings. (OSA's = online sexual activity, which was porn for 99% of subjects.) Interestingly, 20.3% of participants said that one motive for their porn use was "to maintain arousal with my partner." An excerpt:

"This study is the first to directly investigate the relationships between sexual dysfunctions and problematic involvement in OSAs. Results indicated that higher sexual desire, lower overall sexual satisfaction, and lower erectile function were associated with problematic OSAs (online sexual activities). These results can be linked to those of previous studies reporting a high level of arousability in association with sexual addiction symptoms (Bancroft & Vukadinovic, 2004; Laier et al., 2013; Muise et al., 2013)."

6) Adolescents and web porn: a new era of sexuality (2015) - This Italian study analyzed the effects of Internet porn on high school seniors, co-authored by urology professor Carlo Foresta, president of the Italian Society of Reproductive Pathophysiology. The most interesting finding is that 16% of those who consume porn more than once a week report abnormally low sexual desire compared with 0% in non-consumers (and 6% of those who consume less than once a week).

7) Novelty, conditioning and attentional bias to sexual rewards" (2015). Cambridge University fMRI study reported greater habituation to sexual stimuli in compulsive porn users. An excerpt:

Online explicit stimuli are vast and expanding, and this feature may promote escalation of use in some individuals. For instance, healthy males viewing repeatedly the same explicit film have been found to habituate to the stimulus and find the explicit stimulus as progressively less sexually arousing, less appetitive and less absorbing (Koukounas and Over, 2000). ... We show experimentally what is observed clinically that Compulsive Sexual Behavior is characterized by novelty-seeking, conditioning and habituation to sexual stimuli in males.

From the related press release:

They found that when the sex addicts viewed the same sexual image repeatedly, compared to the healthy volunteers they experienced a greater decrease of activity in the region of the brain known as the dorsal anterior cingulate cortex, known to be involved in anticipating rewards and responding to new events. This is consistent with 'habituation', where the addict finds the same stimulus less and less rewarding – for example, a coffee drinker may get a caffeine 'buzz' from their first cup, but over time the more they drink coffee, the smaller the buzz becomes.

This same habituation effect occurs in healthy males who are repeatedly shown the same porn video. But when they then view a new video, the level of interest and arousal goes back to the original level. This implies that, to prevent habituation, the sex addict would need to seek out a constant supply of new images. In other words, habituation could drive the search for novel images.

"Our findings are particularly relevant in the context of online pornography," adds Dr Voon. "It's not clear what triggers sex addiction in the first place and it is likely that some people are more pre-disposed to the addiction than others, but the seemingly endless supply of novel sexual images available online helps feed their addiction, making it more and more difficult to escape."

8) Men's Sexual Life and Repeated Exposure to Pornography. A New Issue? (2015)

Mental health specialists should take in consideration the possible effects of pornography consumption on men sexual behaviors, men sexual difficulties and other attitudes related to sexuality. In the long term pornography seems to create sexual dysfunctions, especially the individual’s inability to reach an orgasm with his partner. Someone who spends most of his sexual life masturbating while watching porn engages his brain in rewiring its natural sexual sets so that it will soon need visual stimulation to achieve an orgasm.

Many different symptoms of porn consumption, such as the need to involve a partner in watching porn, the difficulty in reaching orgasm, the need for porn images in order to ejaculate turn into sexual problems. These sexual behaviors may go on for months or years and it may be mentally and bodily associated with the erectile dysfunction, although it is not an organic dysfunction. Because of this confusion, which generates embarrassment, shame and denial, lots of men refuse to encounter a specialist

Pornography offers a very simple alternative to obtain pleasure without implying other factors that were involved in human’s sexuality along the history of mankind. The brain develops an alternative path for sexuality which excludes “the other real person” from the equation. Furthermore, pornography consumption in a long term makes men more prone to difficulties in obtaining an erection in a presence of their partners.

9) Masturbation and Pornography Use Among Coupled Heterosexual Men With Decreased Sexual Desire: How Many Roles of Masturbation? (2015) - Frequent porn was related with decreased sexual desire and low relationship intimacy. Excerpts:

Among men who masturbated frequently, 70% used pornography at least once a week. A multivariate assessment showed that sexual boredom, frequent pornography use, and low relationship intimacy significantly increased the odds of reporting frequent masturbation among coupled men with decreased sexual desire.

Among men [with decreased sexual desire] who used pornography at least once a week [in 2011], 26.1% reported that they were unable to control their pornography use. In addition, 26.7% of men reported that their use of pornography negatively affected their partnered sex.

10) Associative pathways between pornography consumption and reduced sexual satisfaction (2017) - While this paper links porn use to lower sexual satisfaction, it also reported that frequency of porn use was related to a preference (or need?) for porn over people to achieve sexual arousal. Excerpt:

Finally, we found that frequency of pornography consumption was also directly related to a relative preference for pornographic rather than partnered sexual excitement. Participants in the present study primarily consumed pornography for masturbation. The more frequently pornography is used as an arousal tool for masturbation, the more an individual may become conditioned to pornographic as opposed to other sources of sexual arousal.

11) “I think it has been a negative influence in many ways but at the same time I can’t stop using it”: Self-identified problematic pornography use among a sample of young Australians (2017) - Online survey of Australians, aged 15-29. Those who had ever viewed pornography (n=856) were asked in an open-ended question: ‘How has pornography influenced your life?’ Excerpt:

Among participants who responded to the open-ended question (n=718), problematic usage was self-identified by 88 respondents. Male participants who reported problematic usage of pornography highlighted effects in three areas: on sexual function, arousal and relationships.

12) Study sees link between porn and sexual dysfunction (2017) - The findings of an upcoming study presented at the American Urological Association's annual meeting. A few excerpts:

Young men who prefer pornography to real-world sexual encounters might find themselves caught in a trap, unable to perform sexually with other people when the opportunity presents itself, a new study reports. Porn-addicted men are more likely to suffer from erectile dysfunction and are less likely to be satisfied with sexual intercourse, according to survey findings presented Friday at the American Urological Association's annual meeting, in Boston.

The rates of organic causes of erectile dysfunction in this age cohort are extremely low, so the increase in erectile dysfunction that we have seen over time for this group needs to be explained," Christman said. "We believe that pornography use may be one piece to that puzzle.

13) Exploring the effect of sexually explicit material on the sexual beliefs, understanding and practices of young men: A qualitative survey (2016). A qualitative study reports escalation into extreme material. An excerpt:

Findings suggest that the key themes are: increased levels of availability of SEM, including an escalation in extreme content (Everywhere You Look) which are seen by young men in this study as having negative effects on sexual attitudes and behaviours (That's Not Good). Family or sex education may offer some ‘protection’ (Buffers) to the norms young people see in SEM. Data suggests confused views (Real verses Fantasy) around adolescents’ expectations of a healthy sex life (Healthy Sex Life) and appropriate beliefs and behaviours (Knowing Right from Wrong). A potential causal pathway is described and areas of intervention highlighted.

14) Shifting Preferences In Pornography Consumption (1986) - Six weeks of exposure to nonviolent pornography resulted in subjects having little interest in vanilla porn, electing to almost exclusively watch "uncommon pornography" (bondage, sadomasochism, bestiality). An excerpt:

Male and female students and nonstudents were exposed to one hour of common, nonviolent pornography or to sexually and aggressively innocuous materials in each of six consecutive weeks. Two weeks after this treatment, they were provided with an opportunity to watch videotapes in a private situation. G-rated, R-rated, and X-rated programs were available. Subjects with considerable prior exposure to common, nonviolent pornography showed little interest in common, nonviolent pornography, electing to watch uncommon pornography (bondage, sadomasochism, bestiality) instead. Male nonstudents with prior exposure to common, nonviolent pornography consumed uncommon pornography almost exclusively. Male students exhibited the same pattern, although somewhat less extreme. This consumption preference was also in evidence in females, but was far less pronounced, especially among female students.

15) The Relationship between Frequent Pornography Consumption, Behaviors, and Sexual Preoccupancy among Male Adolescents in Sweden (2017) - Porn use in 18-year old males was universal, and frequent porn users preferred hard-core porn. Does this indicate escalation of porn use?

Among frequent users, the most common type of pornography consumed was hard core pornography (71%) followed by lesbian pornography (64%), while soft core pornography was the most commonly selected genre for average (73%) and infrequent users (36%). There was also a difference between the groups in the proportion who watched hard core pornography (71%, 48%, 10%) and violent pornography (14%, 9%, 0%).

The authors suggest that frequent porn may ultimately lead to a preference for hard-core or violent pornography:

It is also noteworthy that a statistically significant relationship was found between fantasizing about pornography several times a week and watching hard core pornography. Since verbal and physical sexual aggression is so commonplace in pornography, what most adolescents considered hard core pornography could likely be defined as violent pornography. If this is the case, and in light of the suggested cyclical nature of sexual preoccupancy in Peter and Valkenburg, it may be that rather than ‘purging’ individuals of their fantasies and inclinations of sexual aggression, watching hard core pornography perpetuates them, thereby increasing the likelihood of manifested sexual aggression.

16) Out-of-control use of the internet for sexual purposes as behavioural addiction? An upcoming study (presented at the 4th International Conference on Behavioral Addictions, February 20–22, 2017) which also directly asked about tolerance and withdrawal. It found both in "pornography addicts". 

Background and aims: There is an ongoing debate whether excessive sexual behaviour should be understood as a form of behavioural addiction (Karila, Wéry, Weistein et al., 2014). The present qualitative study aimed at analysing the extent to which out-of-control use of the internet for sexual purposes (OUISP) may be framed by the concept of behavioural addiction among those individuals who were in treatment due to their OUISP.

Methods: We conducted in-depth interviews with 21 participants aged 22–54 years (Mage = 34.24 years). Using a thematic analysis, the clinical symptoms of OUISP were analysed with the criteria of behavioural addiction, with the special focus on tolerance and withdrawal symptoms (Griffiths, 2001).

Results: The dominant problematic behaviour was out-of-control online pornography use (OOPU). Building up tolerance to OOPU manifested itself as an increasing amount of time spent on pornographic websites as well as searching for new and more sexually explicit stimuli within the non-deviant spectrum. Withdrawal symptoms manifested themselves on a psychosomatic level and took the form of searching for alternative sexual objects. Fifteen participants fulfilled all of the addiction criteria.

Conclusions: The study indicates a usefulness for the behavioural addiction framework

Finally, a porn user "wiring his sexual response to internet porn" is seen not only in porn-induced sexual dysfunctions and escalation, but neurologically in sensitization (cue-reactivity, cravings, compulsion to use). Sensitization results in increased "wanting" or craving while liking or pleasure diminishes. There are now 20 studies reporting sensitization, cravings, or cue-reactivity in porn users/sex addicts: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20.


SLIDE 8

Real sex, in contrast, is: Courtship, Touching, Being touched, Smells, Pheromones, Less forceful stimulation, Emotional connection, Interaction with a person. What happens when our guy finally gets with a real partner?

ORIGINAL SUPPORT:

This slide contends that masturbating to streaming porn via tube sites is not the same as sex with a real partner. While this is common sense, the core concept is that young men who use streaming porn can condition their sexual arousal to everything associated with their porn use. The disparity between real sex and masturbating to Internet porn is a key factor behind porn-induced sexual dysfunctions (erectile dysfunction, anorgasmia, low libido, delayed ejaculation), as addressed in later slides. The original support came from hundreds of thousands of self reports taken from porn recovery forums and forums unrelated to porn where men posted about porn use affecting their sexual functioning (list of such forums). Again, these thousands of accounts aligned with psychiatrist Norman Doidge's 2007 bestseller, "The Brain That Changes Itself," which also pointed out that internet porn use can alter the sexual template. Excerpts in support of this slide:

The current porn epidemic gives a graphic demonstration that sexual tastes can be acquired. Pornography, delivered by high-speed Internet connections, satisfies every one of the prerequisites for neuroplastic change. ...

Pornography seems, at first glance, to be a purely instinctual matter: sexually explicit pictures trigger instinctual responses, which are the product of millions of years of evolution. But if that were true, pornography would be unchanging. The same triggers, bodily parts and their proportions, that appealed to our ancestors would excite us. This is what pornographers would have us believe, for they claim they are battling sexual repression, taboo, and fear and that their goal is to liberate the natural, pent-up sexual instincts.

But in fact the content of pornography is a dynamic phenomenon that perfectly illustrates the progress of an acquired taste. Thirty years ago, "hardcore" pornography usually meant the explicit depiction of sexual intercourse between two aroused partners, displaying their genitals. "Softcore" meant pictures of women, mostly, on a bed, at their toilette, or in some semi-romantic setting, in various states of undress, breasts revealed.

Now hardcore has evolved and is increasingly dominated by the sadomasochistic themes of forced sex, ejaculations on women's faces, and angry anal sex, all involving scripts fusing sex with hatred and humiliation. Hardcore pornography now explores the world of perversion, while softcore is now what hardcore was a few decades ago, explicit sexual intercourse between adults, now available on cable TV. The comparatively tame softcore pictures of yesteryear—women in various states of undress—now show up on mainstream media all day long, in the pornification of everything, including television, rock videos, soap operas, advertisements, and so on.

Hardcore porn unmasks some of the early neural networks that formed in the critical periods of sexual development and brings all these early, forgotten or repressed elements together to form a new network, in which all the features are wired together. Porn sites generate catalogs of common kinks and mix them together in images. Sooner or later the surfer finds a killer combination that presses a number of his sexual buttons at once. Then he reinforces the network by viewing the images repeatedly, masturbating, releasing dopamine and strengthening these networks. He has created a kind of "neosexuality," a rebuilt libido that has strong roots in his buried sexual tendencies. Because he often develops tolerance, the pleasure of sexual discharge must be supplemented with the pleasure of an aggressive release, and sexual and aggressive images are increasingly mingled--hence the increase in sadomasochistic themes in hardcore porn.

Typically, while I was treating one of these men for some other problem, he would report, almost as an aside and with telling discomfort, that he found himself spending more and more time on the Internet, looking at pornography and masturbating. He might try to ease his discomfort by asserting that everybody did it. In some cases he would begin by looking at a Playboy-type site or at a nude picture or video clip that someone had sent him as a lark. In other cases he would visit a harmless site, with a suggestive ad that redirected him to risque sites, and soon he would be hooked. ...

A number of these men also reported something else, often in passing, that caught my attention. They reported increasing difficulty in being turned on by their actual sexual partners, spouses or girlfriends, though they still considered them objectively attractive. When I asked if this phenomenon had any relationship to viewing pornography, they answered that it initially helped them get more excited during sex but over time had the opposite effect. Now, instead of using their senses to enjoy being in bed, in the present, with their partners, lovemaking increasingly required them to fantasize that they were part of a porn script. Some gently tried to persuade their lovers to act like porn stars, and they were increasingly interested in “fucking” as opposed to “making love.” Their sexual fantasy lives were increasingly dominated by the scenarios that they had, so to speak downloaded into their brains, and these new scripts were often more primitive and more violent than their previous sexual fantasies. I got the impression that any sexual creativity these men had was dying and that they were becoming addicted to Internet porn.

The changes I observed are not confined to a few people in therapy. A social shift is occurring.

UPDATED SUPPORT:

This large section from a 2017 review of the literature, Pornography, Pleasure, and Sexuality: Towards a Hedonic Reinforcement Model of Sexually Explicit Internet Media Use, contends that internet porn use (IPU) might lead to preference over partnered sex:

Why IPU might increase self-focused, hedonic sexual motivations?

Central to the notion that IPU increases self-focused and hedonic sexual motivations is the supposition that IP, because of its uniquely rewarding properties, alters the relative reinforcement of partnered sexual activity. Humans engage in calculations of the effort required to obtain a specific reward (Green & Myerson, 2004; Kahneman, 2003). When the reward is deemed worthy of a certain amount of effort, the effort is undertaken. When adjustments to this ratio are made, behaviors and motivations change as a result. Returning to our parallel example of hunger drive and food, there is abundant evidence that changes to the rewarding nature of food changes behavior that is readily observable on a cultural/societal scale. The proliferation of highly palatable foods in the form of low-cost, easily accessible “junk food” is well documented in the literature (see Monteiro, Moubarac, Cannon, Ng, & Popkin, 2013). The abundance of highly palatable foods has been associated with increased consumption of such foods and a per-capita decrease in consumption of healthy—but more expensive and less palatable—options (Drewnowski & Specter, 2004; Hardin-Fanning & Rayens, 2015). In short, the popularity of easily accessible and intensely rewarding highly palatable foods has had cultural impacts on the way in which people approach food.

It is likely that a similar process is occurring with IPU. Although solitary sexual activity (e.g., IPU) and dyadic sexual activity both involve a cue/stimulus (e.g., sexually explicit imagery or sexual partner) and a clear goal of sexual gratification (e.g., orgasm), the methods by which that gratification is obtained are different, with solitary sexual activity clearly implying a self-focused hedonic process (e.g., masturbation). Although one might speculate that viewing IP or masturbating are less preferred relative to partnered sexual activity, the ease and accessibility of IP may make them more appealing to some individuals (e.g., Wright, Sun, Steffen, & Tokunaga, 2017), as may the novelty and customizability of IP.

Importantly, if this supposition—that IPU predicts an increase in self-focused and hedonic sexual motives— is true, it should be evident in the sexual attitudes and behaviors associated with IPU. Specifically, we would expect to find an association between IPU and more pleasure-focused attitudes toward sexuality, such as openness to casual sexual encounters and a focus on personal pleasure preferences. We would also expect IPU to be associated with more objectifying or instrumental views of prospective sexual partners, as sexual objectification is inherently self-focused and hedonistic, viewing prospective partners as means to an end (e.g., sexual pleasure) rather than relational investments (Wright & Tokunaga, 2016). There would also be associations with greater individual emphasis on personal sexual satisfaction. Finally, we would expect to find that IPU is associated with more diverse and potentially risky sexual behaviors and more specific sexual preferences that are all in service of enhancing personal sexual pleasure.

Evidence of IPU’s Impacts on Sexual Motivation

We have made the theoretical argument that IPU is likely associated with changes in human sexual motivation. Below, we seek to review the known attitudinal and behavioral correlates and outcomes of IPU in order to evaluate whether they support the hypothesized relationship.

Casual Sexual Behavior.

One particular evidence of a more hedonic and self-focused approach to sexuality would be increases in uncommitted sexual behaviors (e.g., casual sex with consenting partners). Uncommitted sexual behavior is commonly associated with pleasure-seeking motives (Garcia & Reiber, 2008; Kruger & Fisher, 2008; Sirin, McCreary, & Mahalik, 2004). People who engage in uncommitted sexual behavior often describe hedonistic goals as the primary motivation for such encounters (Armstrong & Reissing, 2015; Lyons, Manning, Longmore, & Giordano, 2014; Regan & Dreyer, 1999) and often explicitly deny social sexual motivations as reasons for such encounters (Lyons et al., 2014). As such, uncommitted sexual behavior is likely a strong indication of greater hedonic or self-focused sexual motivation, particularly among men (Regan & Dreyer, 1999), although women also frequently report hedonic motivations for such encounters (Lyons et al., 2014).

In a longitudinal panel study of General Social Survey (GSS) participants in the U.S. (Wright, Tokunaga, & Bae, 2014), two samples were surveyed at two time-points over two years (Sample 1, N=269, Mage=47.0, SD=14.8, 37% men, sampled at 2006 and 2008; Sample 2, N=282, Mage=49.9, SD=14.0, 50.1% men, sampled at 2008 and 2010). Over time, the use of sexually explicit media (not directly defined as internet use only) was associated with increases in sexual permissiveness and more open attitudes toward extramarital sexual behaviors. Notably, this association persisted, above and beyond baseline attitudes, suggesting that pornography use is predictive of such attitudes. Additionally, the pattern was not evident in reverse (e.g., extramarital openness did not predict pornography use over time), suggesting that the relationship between the two variables is not bidirectional.

These findings also extend to actual behaviors as well. Analyses from nationally representative samples (General Social Survey) have linked increased use of sexually explicit materials to more engagement in casual sexual behaviors over time (Wright, 2012). Notably, these associations were not observable in reverse: Pornography use was associated with increasing engagement in casual sexual encounters, but casual sexual encounters were not reciprocally associated with increased pornography use. Although these findings cannot confirm a direct, causal relationship between IPU and casual sex, they do show that increases in IPU precede greater engagement in casual sexual behaviors over time. This temporal relationship is consistent with our model which suggests that IPU leads to a marked increase in hedonic sexual motives and behaviors.         

Evidence supporting a link between IPU and increased casual sexual behavior has also been observed in adolescents. In a study of adolescents in the Southeastern United States (N=967, 49.9% male, Mage=13.6, SD=0.7), greater use of sexually explicit media (5-point ordinal; more than once a week—never) was cross-sectionally associated with more permissive sexual norms and greater acceptance of casual sexual behavior in both men and women (Brown & L’Engle, 2009). Importantly, when sampled again two years later, IPU at baseline was associated with continued tendencies toward greater sexual permissiveness, as well as greater engagement in a variety of sexual behaviors. Such a finding extends previous research that has shown that IPU is predictive of attitudes toward and engagement in non-committed sexual encounters by demonstrating this relationship in adolescence.

In a study of “friends with benefits” (FWB) relationships (Braithwaite, Aaron, Dowdle, Spjut, & Fincham, 2015), in which partners engage in both casual, non-romantic friendship while also being sexually active with one another, IPU emerged as a consistent predictor of non-committed sexual behaviors. Specifically, in a cross-sectional study of undergraduates in the U.S. (Study 1, N=850, 23% men, Mage=19.3, SD=1.3), IPU (8-point ordinal; never—several times a day) was associated with greater likelihood of having engaged in a FWB relationship, greater number of partners with which one had engaged in such relationships, and greater plan to continue such relationships in the future. Additionally, these findings were directly replicated cross-sectionally (Study 2, N=992, 30% men, Mage=19.5., SD=1.3) in another sample of undergraduates, with all associations falling within expected confidence intervals. When these findings were examined longitudinally over a roughly three-month period, the association between IPU and FWB relationships again held, and was stronger than the cross-sectional association between the two behaviors, after adjusting for the stability of FWB relationships. Collectively, these findings point to the conclusion that IPU is a unique and potentially causal factor that influences the likelihood of engaging in casual sexual behaviors.

The links between IPU and casual sexual behavior also appear among college students, for whom casual sexual behavior is generally thought to be more common (Garcia, Reiber, Massey, & Merriwether, 2012). In a study of “hook-up” culture in college campuses (Braithwaite, Coulson, Keddington, & Fincham, 2015), in which college students engage in one-time sexual encounters with non-romantic partners, links were again found between IPU (8-point ordinal; never—several times a day) and casual sexual behaviors. Using the same samples as described above (Braithwaite, Aaron, et al., 2015), IPU was associated with casual sexual behavior in the form of hookups both cross-sectionally and longitudinally. IPU predicted both the likelihood of having engaged in a hookup, the number of previous hookup partners, and the planned likelihood of engaging in future hookups. As such, there is evidence that IPU is predictive of casual sexual behavior in multiple forms (e.g., non-committed FWB relationships and non-committed one-time sexual encounters).

Beyond these compelling longitudinal findings, there is additional, cross-sectional support for the notion that IPU is associated with increases in casual sexual behaviors. In a cross-sectional study of young adults in the U.S. (N=813, 38% men; Mage=20, SD=1.8), IPU (6-point ordinal; non—every day or almost every day) was commonly reported by both genders (more so among men: 86.1% men vs. 31% of women) and positively associated with acceptance of non-committed sexual behaviors (Carroll et al., 2008). Similarly, in a study of adolescents in the U.S. (Braun-Courville & Rojas, 2009; N=433, 85% women, Mage= 18; SD=2.1) IPU (4-point ordinal; none—more than 10 times) was associated with a greater history of casual sexual encounters and more permissive attitudes toward future casual sexual encounters. Finally, in a large, cross-sectional study of Dutch adolescents (Peter & Valkenburg, 2009; N=2,343, 51% men; Mage=16.4, SD=2.29), IPU (7-point ordinal; neverseveral times per day) was associated with greater sexual permissiveness and acceptance of non-committed sexual exploration in the future.

Outside of Western contexts, these findings persist. In a cross-sectional study of university students (N=556; 73.4% women) in a predominantly Muslim society with strict anti-pornography laws (Indonesia; Hald & Mulya, 2013), IPU (standardized index of frequency and time spent) was predictive of non-committed sexual behaviors and extramarital sexual behaviors. Notably, these findings were evident for male participants only, despite no differences in incident rates in men and women for sexual behaviors in general. Additionally, in a sample of Taiwanese adolescents (N=2,001; 50% male; Mage=15.6, SD=0.9) found that internet pornography exposure (Lo & Wei, 2005; 5-point ordinal scale; nevernearly every day) was cross-sectionally associated with and predictive of more sexually permissive attitudes and behaviors (e.g., casual sex). Finally, in a cross-sectional analysis of men in Hong Kong (Lam & Chan, 2007; N=229, Mage=21.5, SD=1.8), IPU (4-point ordinal scale; NeverFrequently) was positively associated with sexual permissiveness and proclivity to engage in sexual harassment.

Collectively, these findings indicate that there is likely an association between IPU and both attitudes toward and engagement in casual sexual behavior. Furthermore, given that many of these findings are longitudinal and nationally representative in nature, they provide stronger evidence for the conclusion that IPU is predictive of increased hedonic motivations for sexual activity.

Sexual Objectification.

More evidence of IP’s influence on egocentric and hedonic sexual motivation may be found in research related to IP and sexual objectification. Sexual objectification, by nature, involves the devaluation of the personhood of prospective sexual partners and the view of them as objects for personal pleasure enhancement (Fredrickson & Roberts, 1997). This is especially true of heterosexual men, for whom sexual objectification has been primarily researched (e.g., Fredrickson & Roberts, 1997; Szymanski, Moffit, & Carr, 2010). However, both men and women may view others as sexual objects (Strelan & Hargreaves, 2005), and, although understudied in LGBTQ populations, there is evidence that such individuals may also objectify prospective partners (Wilson et al., 2009). Should one approach partnered sexual activity from an exclusively self-focused and hedonic perspective, it is quite likely that one would also view prospective sexual partners as sexual objects by which greater sexual pleasure can be obtained (Wright & Tokunaga, 2015, 2016). Therefore, one indicator of the association between IPU and increased hedonic motivation would be an increase in sexual objectification associated with such use.

Published literature on the use of sexually explicit media and attitudes toward women generally shows that the use of sexually explicit media is associated with greater acceptance of violence toward women (Allen, Emmers, Gebhardt, & Giery, 1995; Demare, Briere, & Lips, 1988; Hald, Malamuth, & Yuen, 2010), particularly among men already predisposed to engage in sexual violence (Malamuth, Hald, & Koss, 2012). Moreover, in a meta-anaytic study of the effects of pornography use on sexual attitudes (Wright, Tokunaga, & Kraus, 2016), pornography consumption in both men and women was associated with more sexually aggressive attitudes. Building on this, in a longitudinal study of Dutch adolescents (N=962, Range=14-20; Peter & Valkenburg, 2009), IPU (7-point ordinal; neverseveral times a day) predicted general notions of women as sexual objects among both men and women. However, it was noted that only among men did such increased views of women as sexual objects then predict increases in IPU. In short, for male participants, IPU was longitudinally linked to greater sexual objectification of women, which was, in turn, longitudinally linked to greater IPU.

Pornography exposure has also been shown to predict sexually objectified attitudes toward women in experimental and correlational research conducted with collegiate males in the United States (Wright & Tokunaga, 2015, 2016). For instance, in a sample of undergraduate men (N=133, Mage=20.91, SD=1.84), participants who did not generally consume sexually explicit media and who were shown digital images of centerfolds from a popular pornographic website (compared to individuals shown images of sports) reported increased desires for non-relational sex, increased importance of physical attractiveness in prospective partners, and more views of women as sexual objects for the purpose of gaining pleasure (Wright & Tokunaga, 2015).

Internationally, IPU (6-point ordinal; never—every day) specifically has also been correlated with objectifying women among college students (N=476; 40.3% men, Mage=19.5, SD=1.3) in Japan (Omori et al., 2011). Collectively, these findings suggest that, particularly for heterosexual men, IPU is cross-sectionally, longitudinally, and experimentally associated with increases in sexual objectification, which is consistent with more self-focused and hedonic views of sexual activity.

Sexual Preferences.

An increase in hedonic sexual motivation because of IPU would also be evident in individual’s sexual preferences. Hedonic drives are known to be associated with a desire for variety and novelty (Kashdan & Steger, 2007; Holbrook & Hirschman, 1982). A similar understanding may also be applied to sexual preferences and practices (discussed later). Specifically, increases in hedonic sexual drives may also be associated with increases in specific, novel, varied, and self-focused sexual preferences.

In a cross-sectional study (Morgan, 2011) of college students in the Northwest (N=782, 41.7% men, Mage=19.9, Range=18-30), regular IPU (10-point ordinal; nevermore than once a day) was associated with greater variety in sexual preferences and a greater preference for a variety of sexual practices (e.g., using toys or props; playful domination/submission; trying novel positions). Notably, IPU was robustly predictive of a variety of sexual preferences that extended beyond real life sexual experience history. Regular users tended to report a desire to engage in a wide variety of sexual experiences, even if they had previously had no experience with such behaviors. Such a finding indicates that IPU may be influencing sexual desire and motivation or that people who report a variety of sexual preferences are also more open to IP.

Building on this, in a cross-sectional study (Sun, Bridges, Johnson, & Ezzell, 2016) of undergraduate men (N=479, Range=18-29), IPU (8-point ordinal; never—daily or almost daily) was substantially associated with various sexual preferences and scripts that are hedonically driven. IPU predicted the likelihood that an individual would request specific sexual acts seen in IP from a real-life partner and the likelihood that pornography would be integrated into sexual encounters as a supplement to enhance arousal. In short, IPU was associated with a desire to recreate or incorporate what was seen in partnered sexual interaction.

Similarly, in cross-sectional samples of internet using undergraduates (Bridges, Sun, Ezzell, & Johnson, 2016; N=1,883; 38.6% men; Mage=22.6, SD=8.0), IPU (8-point ordinal; never—daily or almost daily) was associated with the desire to try specific sexual practices commonly seen in pornographic content (e.g., men spanking their partners, facial ejaculation, anal penetration). Similar findings have also been observed in cross-sectional studies of German men (Wright, Sun, Steffen, & Tokunaga, 2015; N=384, Mage=32.1, SD=9.1) and women (Sun, Wright, & Steffen, 2017; N=392, Mage=27.5, SD=6.7), with IPU (8-point ordinal; never—daily or almost daily) in both genders being associated with a desire to engage in specific sexual practices seen in IP. Furthermore, in studies of Dutch adolescents (Hald, Kuyper, Adam, & Wit, 2013; N=4,600; 30.5% men; Range= 15-25), IPU (5-point ordinal; neverdaily) was positively predictive of a desire to have more “adventurous sex” in real life (e.g., multiple partners at the same time; meeting online partners for real-life encounters), even when other explanatory variables (e.g., thrill-seeking, sexual sensation-seeking, assertiveness, sexual self-esteem, religiousness) were controlled.

Experimentally there is also evidence that IPU is associated with increased hedonic sexual motivation. For example, in early work on this topic (E.g., Zillman & Bryant, 1988a, 1988b), pornography use in general (not necessarily just IP) has been linked with greater preference for sexual novelty, new sexual partners, and non-committed sexual relationships. Regarding IP specifically, in previously described experimental procedures (Wright & Tokunaga, 2015) found that exposure to IP predicted more hedonistic preferences as well, such as more attractive partners. Collectively, such findings suggest that IP may be causing increases in hedonic sexual preferences.

These findings are further substantiated in both quantitative and qualitative research samples. In a cross-sectional, interview-based study of undergraduates (N=172; 41% men; Mage=21.3; Range=18-34; Weinberg, Williams, Kleiner, & Irizarry, 2010), IP exposure was associated with increased openness to a variety of sexual acts, including oral-genital contact, the use of mechanical enhancements (i.e., sex toys), openness to anal sexual stimulation, and the desire to engage in multi-partner sexual encounters (i.e., three-way sexual encounters). Notably, these findings were particularly consistent for heterosexual men and women. Moreover, in a follow-up, qualitative study with undergraduates (N=73, 26% men; Weinberg et al., 2010), responses to open-ended questionnaires reflected similar relationships between IP exposure and openness to a variety of sexual acts. Free response answers from both men and women reflected a causal understanding of the relationship between their IPU and sexual preferences, noting that IP had normalized a wide range of sexual behaviors and enhanced their personal openness to engaging in such behaviors. In short, although the majority of literature linking IPU to more hedonic sexual preferences is cross-sectional, retrospective reports suggest that people understand such links as causal in nature. Although the biases of retrospective self-report are well-known (Chan, 2009), IP consumers seem to believe that their use has altered their behavior in hedonic ways, which provides some support to our model.

Sexual Risk-Taking.

Studies associating pornography consumption with sexual risk behavior may also be indicative of self-focused and hedonic motivations, as risky sexual behaviors are often motivated by a desire for short-term sexual pleasure with little regard for potential consequences (Cooper et al., 1998). With greater hedonism, people are more likely to take risks to experience pleasure (Broadbeck, Vilén, Bachmann, Znoj, & Alasker, 2010; O’Leary et al., 2005). As such, links between IPU and sexual risk-taking can be cited as further evidence for the relationship between IPU and reinforced hedonic motivation.

Longitudinally, results from a nationally representative, 2008, two-wave panel study of adults (N=833) and adolescents (N=1,445) in Holland (Peter & Valkenburg, 2011b) suggested that, for both adults and adolescents, IPU (7-point ordinal; never—several times a day) was associated with greater sexual risk taking. Cross-sectionally, within both samples, there were small positive correlations between IPU and unsafe sexual practices (i.e., unprotected sex). Over a six-month period, IPU was unrelated to risky sexual behaviors in adolescents, but positively predictive of risky sexual behavior in adults, above and beyond the predictive influence of baseline risky sexual behaviors. Additionally, no reciprocal relationship was found (i.e., risky sexual behavior did not predict IPU over time), suggesting that IPU may be driving increases in risky sexual behavior, but not the inverse.

In a study of men in the U.S. who have sex with men (N=149), a notable association between IPU and risky sexual behavior was found (Eaton, Cain, Pope, Garcia, & Cherry, 2012). Specifically, in a sample of HIV negative men participating in a risk-reduction intervention, IPU (weekly use in minutes; 8-point ordinal; 0 minutes—180 minutes or more) was associated with a greater likelihood of having had recent unprotected sex and a greater number of partners with whom unprotected sex had occurred. Additionally, IPU was associated with greater substance use (a potential facilitator of risky sexual behavior; Cooper, 2002) and decreased estimation of HIV infection risk.

In a large-scale, cross-sectional study of non-monogamous men who have sex with men (N=751; Median Age =32; Range=18-68), there was a positive association between viewing risky sexual behaviors in IP and real-life engagement in such risky sexual behaviors (Stein, Silvera, Hagerty, & Marmor, 2012). Specifically, men who reported having witnessed unprotected anal intercourse in IP were also more likely to endorse engaging in such behaviors in their real-life sexual encounters.

Building on these findings, in a qualitative study of men who have sex with men (N=79; Mage=not reported), structured interviews revealed three mechanisms by which IPU may lead to riskier sexual behaviors (Wilkerson et al., 2012). Specifically, iterative coding procedures using standard techniques (e.g., industry standard coding software, multiple reporters, quality checks, and debriefing with participants) revealed that the likelihood that a sexual behavior or risky sexual practice witnessed in IP might lead to a real life sexual behavior was a function of the participants’ arousal when watching that specific IP, their perceptions of pleasure from watching the IP, and the availability and willingness of a trusted sexual partner to engage in that IP. When participants found acts depicted in IP to be arousing and pleasurable (in appearance), and when a trusted sexual partner was available, riskier sexual behaviors were reported as a likely result.

In a cross-sectional study of adolescents in New York City (N=433; 85% female; Mage=18, SD=2.1, Range=12-22), IPU (4-point ordinal; none—more than 10 times) was associated with a wide variety of risky sexual behaviors (Braun-Courville & Rojas, 2009). Specifically, IPU was positively associated with greater frequency of sexual intercourse, more lifetime partners, more partners within the past three months, greater likelihood of using alcohol or illicit substances during intercourse, greater likelihood to have had anal sex, and with overall sexual risk scores. No association was found between IPU and condom use. However, cross-sectional research in other samples (e.g., Wright, Tokunaga, & Kraus, 2016; Study 1, N=310, 54.5% men; Mage=20.4, SD= 1.8; Study 2, N=418, 78.7% women; Mage=21.2, SD=2.8) has found that pornography use (predominately IP) was associated with less frequent use of condoms during sexual encounters and lower estimation of peer condom use (i.e., believing that condom use is generally less common).

These findings also extend beyond Western contexts. In a large-scale study of college students in China (N=19,123; 48.7% male, Mage=20.8, SD=1.5), IPU (unspecified measurement) was associated with several sexual behaviors and attitudes that might be considered risky (Sun et al., 2013). Specifically, for both men and women IPU was associated positive attitudes toward risky sexual behaviors such as not using condoms. Similarly, in a large-scale study of male migrant workers in India (N=11,219, 100% men, Mage=26.6, SD=5.5), having viewed pornographic videos in general was associated with a greater likelihood of engaging in paid sex, experience of an STI, and inconsistent use of condoms (Mahapatra & Saggurti, 2014).

Beyond standard convenience samples, these findings are also apparent in nationally representative studies. Regarding IPU specifically, in analyses based on the 2000, 2002, and 2004 General Social Surveys (Wright & Randall, 2012), male participants (N=1,079; Mage=14.2; SD=14.1) who acknowledged viewing IP (4-point ordinal, past 30 days; never—more than five times) also endorsed a variety of other riskier sexual behaviors including having multiple partners, engaging extramarital sex, and paying for sex. Analyses of women during the same time period (2000-2004) found that women who acknowledged IPU were more likely to report having multiple sexual partners (Wright & Arroyo, 2013). Interestingly, for men, there was no association between IPU and condom use (Wright & Randall, 2012), a metric typically used as a benchmark for safe sexual practices (Albarracin, Johnson, Fishbein, & Muellerleile, 2001). Similarly, in an analysis of over 37 years of data from the GSS (1973-2010; Wright, 2013a), pornography use in general—not just IP— in men was associated with more sexual partners over the lifetime and greater likelihood of having solicited or paid for a sexual encounter. Analyses of women’s use of pornography in the GSS over the same time period (1973-2010) found that women who used pornography were also more likely to report having extramarital sex, having paid sex, and having multiple sexual partners (Wright, Bae, & Funk, 2013).

Similar patterns are also observable in regards to substance use during sexual encounters and condom use during sexual encounters (Braithwaite, Givens, Brown, & Fincham, 2015). In a cross-sectional study of college students (N=1216; 37% men; Men-Mage=19.6, SD=1.4; Women-Mage=19.2, SD=1.15), IPU (8-point ordinal; never—several times a day) was associated with intoxication during uncommitted sexual encounters, with men specifically demonstrating a pattern of greater IPU being associated with greater intoxication. Additionally, it was also associated with a higher incidence of unprotected (e.g., no condom) penetrative sexual encounters while intoxicated, a particularly risky sexual behavior.

In contrast to the above findings, findings that include samples from other countries have been less convincing in identifying a relationship between IPU and risky sexual behaviors. In a study of internet-using Swiss adolescents (N=7,458, 51.5% male; Luder et al., 2011), there were no associations found between IP exposure (intentional or unintentional) and risky sexual behaviors for either male or female participants, except for condom use among males. For males, intentional exposure to IP was associated with a reduced likelihood to have used a condom during the most recent sexual encounter. Similarly, in a previously described study of Croatian young adults (N=1,005), there were again unclear links between IPU and risky sexual behaviors (Sinkovic et al., 2013). Within this sample, frequency of IPU and personal importance of IPU were not predictors of various risky sexual behaviors. However, age at first exposure to IP was a significant, but weak, predictor of sexual risk taking, with earlier age of exposure being associated with greater risk taking. These two studies do represent an important divergence from the previously described literature that links IPU with greater sexual risk taking. However, given that these two studies occurred among adolescents and young adults in two European countries and represent two cross-sectional divergences from a clear and compelling body of longitudinal and cross-sectional research, we are hesitant to speculate about the natures of the differences. Furthermore, data involving Swiss adolescents (Luder et al., 2011) was collected in 2002, which predates the widespread promulgation of streaming pornography services that allow for the novelty and variety in IP previously described.

Collectively, across several studies using a variety of samples and methodologies, IPU seems to be consistently, positively related to risky sexual behaviors. Although some unclear findings are present (e.g., Sinkovic et al., 2013; Luder et al., 2011) the majority of studies find positive and predictive associations between IPU and sexual risk taking. Given this body of evidence, it is perhaps not surprising that previous systematic reviews have similarly concluded that there is a notable, positive relationship between the use of sexually explicit media and risky sexual behavior (Harkness, Mullan, & Blaszcynski, 2015) and that this link is possibly causal in nature.

Delay Discounting.

Finally, if IPU were to be associated with changes in sexual motivation toward more hedonic and self-focused drives, we would expect to find that there are basic changes in hedonic self-regulation. We have previously contended that the instantaneous and easily accessible nature of IPU reinforces the instant gratification of sexual desire and drive. There is also evidence that such use may influence individuals’ ability to delay gratification in general (Negash, Sheppard, Lambert, & Fincham, 2016). In a longitudinal study of college students (N=123, 32 men, 91 women; Median Age=20, Range=18-27), IPU was associated with greater propensity to discount future rewards (Negash et al., 2016, Study 1). These findings were further tested in a small experimental study of regular consumers of IP (Negash et al., 2016, Study 2; N=37; 24 men, 13 women). In this study, 16 participants were randomly assigned to refrain from IPU for three weeks, and the remaining 21 were asked to refrain from eating their favorite food for three weeks. After the study period, those who had abstained from IPU demonstrated diminished delay discounting (i.e., an increased ability to choose larger, future rewards, moderate effect, partial η2=.11) compared to those who refrained from their favorite food. These preliminary findings point to a potential tentative links between IPU and delay discounting in general.

Recently, in an experimental study of Taiwanese college students (Cheng & Chiou, 2017; Study 1, N=122, 51% men, Mage=20.9, SD=1.5), IP exposure was again associated with delay discounting. Specifically, compared to controls, individuals exposed to sexually themed online images were more likely to discount the value of future rewards in favor of smaller, immediate rewards, again demonstrating a means by which IPU may be associated with more hedonic motivations.

Summary of Enhanced Hedonic Sexual Motives

In the final step of this proposed model, IP influences sexual motivation, attitudes, and behaviors by strongly reinforcing hedonic sexual motivation. By influencing the relative reinforcement value of sexual reward, IP alters the way that consumers approach sexual activity in both solitary and partnered contexts. Evidence of this alteration is seen in numerous domains.

IPU is associated with more permissive attitudes toward casual sex and more engagement in casual sex, both of which are known to be hedonically motivated. IPU users are more likely to endorse sexually objectifying prospective sexual partners, viewing them as instruments for personal pleasure. IP consumers are also likely to report hedonic sexual motives and preferences that they attribute to their IPU, suggesting that IPU leads to more hedonic sexual preferences. IPU cross-sectionally and longitudinally predicts sexual risk taking, which is another pleasure-focused sexual drive. Finally, IP consumers display greater tendencies toward preferring immediate small rewards, as opposed to future, greater rewards (i.e., delay discounting). Collectively, these findings are consistent with the hypothesis that IPU is driving increases in self-focused, hedonic sexual motives. Finally, given that many of these linkages are longitudinal and others are experimental, these results suggest an understanding of IPU as a causal factor in increasing hedonic sexual motivation.

From an update by Norman Doidge published in a peer-reviewed journal: Sex on the Brain: What Brain Plasticity Teaches About Internet Porn (2014), here are a few excerpts explaining how porn use shapes sexual arousal tastes, especially during critical periods of development:

But the main point is that in our critical periods we can acquire sexual and romantic tastes and inclinations that get wired into our brains and can have a powerful impact for the rest of our lives. And the fact that we can acquire different sexual tastes contributes to some of the tremendous sexual variation between us.

The idea that a critical period helps shape sexual desire in adults contradicts the currently popular argument that what attracts us is not so much the product of our personal history, but solely the effect of our common biology. Models and movie stars, for instance – are widely regarded as universally beautiful or sexy. A certain strand of biology teaches us that some people are attractive because they exhibit biological signs of robustness, which promise fertility and strength: a clear complexion and symmetrical features mean a potential mate is free from disease; an hourglass figure is a sign a woman is fertile; a man’s muscles predict he will be able to protect a woman and her offspring.

“Acquired tastes” are by definition learned, unlike “tastes”, which are inborn. A baby needn’t acquire a taste for milk, water, or sweets; these are immediately perceived as pleasant. Acquired tastes are initially experienced with indifference or dislike but later become pleasant – the odours of cheeses, Italian bitters, dry wines, coffees, pâtés, the hint of urine in a fried kidney. Many delicacies that people pay dearly for, that they must “develop a taste for”, are the very foods that disgusted them as children.

In Elizabethan times lovers were so enamoured of each other’s body odours that it was common for a woman to keep a peeled apple in her armpit until it had absorbed her sweat and smell. She would give this “love apple” to her lover to sniff at in her absence. We, on the other hand, use synthetic aromas of fruits and flowers to mask our body odour from our lovers. Many tastes we think “natural” are acquired through learning and become “second nature” to us. We are unable to distinguish our “second nature” from our “original nature” because our neuroplastic brains, once rewired, develop a new nature, every bit as biological as our original.

Pornography seems, at first glance, to be a purely instinctual matter, and it would seem that there is nothing acquired about it; sexually explicit pictures, of people in their most natural condition, nudity, trigger instinctual responses, which are the product of millions of years of evolution. Furthermore, the mammalian male’s interest in different partners, called “the Coolidge effect”, seems part of our evolutionary heritage. But if that were all there was to it, pornography would be unchanging, except for the fact that men would want new partners. The same triggers, body parts and their proportions, that appealed to our ancestors would excite us. This is what pornographers would have us believe, for they claim they are battling sexual repression, taboo and fear, and that their goal is to liberate the natural, pent-up sexual instincts.

But in fact the content of pornography is a dynamic phenomenon that perfectly illustrates the progress of an acquired taste.


SLIDE 9

Well, researchers don't know much about the effects of Internet porn - for several reasons. In 2009 when Lajeunesse tried to study porn's impact on users, he couldn't find any college-age males who weren't using it. So, the first serious dilemma is that studies have no control groups. This creates a huge blind spot. Imagine if all guys started smoking heavily at age 10 - and there were no groups who didn't. We'd think lung cancer was normal for guys.

ORIGINAL SUPPORT:

Original article on Science Daily, where Lajeunesse said he couldn't find any college-age males who weren't using it.

UPDATED SUPPORT:

1) This 2017 study on Australians ages 15-29 found that 100% of the men had viewed porn. It also reported that more frequent pornography viewing correlated with mental health problems.

2) This 2017 Swedish study reported that 98% of 18-year old males had watched pornography (The Relationship between Frequent Pornography Consumption, Behaviors, and Sexual Preoccupancy among Male Adolescents in Sweden).


SLIDE 10

Undaunted by his lack of non-users, Lajeunesse asked 20 male students - "Is Internet porn affecting you or your attitudes toward women?" Their answer? "Nah, I don't guess it is." But they'd been using it for about a decade…pretty much nonstop. This is like asking a fish what it thinks about water.

ORIGINAL SUPPORT:

Original article on Science Daily, where Lajeunesse said  "Is Internet porn affecting you or your attitudes toward women?"

In 2012 there existed a tremendous amount anecdotal evidence that men's attitudes towards women shift following elimination of porn (pages of such reports are here: Guys Who Gave Up Porn: On Sex and Romance). In addition, the preponderance of empirical evidence at the time reported links between porn use and poorer attitudes towards women. For example:

1) Pornography and Attitudes Supporting Violence Against Women: Revisiting the Relationship in Nonexperimental Studies (2010) – A review of the literature. An excerpt:

A meta-analysis was conducted to determine whether nonexperimental studies revealed an association between men's pornography consumption and their attitudes supporting violence against women. The meta-analysis corrected problems with a previously published meta-analysis and added more recent findings. In contrast to the earlier meta-analysis, the current results showed an overall significant positive association between pornography use and attitudes supporting violence against women in nonexperimental studies. In addition, such attitudes were found to correlate significantly higher with the use of sexually violent pornography than with the use of nonviolent pornography, although the latter relationship was also found to be significant.

2) Pornography and Sexual Callousness and the Trivialization of Rape (1982) – Excerpt:

Explored the consequences of continued exposure to pornography on beliefs about sexuality in general and on dispositions toward women in particular. Found that massive exposure to pornography resulted in a loss of compassion toward women as rape victims and toward women in general.

3) Exposure to pornography and attitudes about women and rape: A correlational study (1986) – Excerpt:

Compared to a group that had watched a control film, male subjects who were shown the violent film agreed more with items endorsing interpersonal violence against women than did the control subjects. However, contrary to predictions, there was no statistically significant difference between the two groups in their acceptance of rape myths, although there was a trend in the predicted direction.

4) Use of pornography and self-reported engagement in sexual violence among adolescents (2005) – Excerpt:

This cross-sectional study examined 804 adolescents, boys and girls, aged from 14 to 19 years, attending different types of high schools in the northwest of Italy. The main goals were: (i) to investigate the relationship between active and passive forms of sexual harassment and violence and the relationship between pornography (reading magazines and viewing films or videos) and unwanted sex among adolescents; (ii) to explore the differences in these relationships with respect to gender and age; and (iii) to investigate the factors (pornography, gender and age) that are most likely to promote unwanted sex. The findings showed that active and passive sexual violence and unwanted sex and pornography were correlated.

5) Relationships among cybersex addiction, gender egalitarianism, sexual attitude and the allowance of sexual violence in adolescents (2007) – Excerpt:

This study was done to investigate cybersex addiction, gender egalitarianism, sexual attitude and the allowance of sexual violence in adolescents, and to identify the relationships among these variables. The participants were 690 students from two middle schools and three high schools in Seoul. Cybersex addiction, gender egalitarianism, sexual attitude and the allowance of sexual violence in adolescents were different according to general characteristics. Gender egalitarianism, sexual attitude and the allowance of sexual violence in adolescents were influenced by cybersex addiction.

6) Adolescents’ Exposure to a Sexualized Media Environment and Their Notions of Women as Sex Objects (2007) – Excerpt:

This study was designed to investigate whether adolescents’ exposure to a sexualized media environment is associated with stronger beliefs that women are sex objects [on-line survey of 745 Dutch adolescents aged 13 to 18]. More specifically, we studied whether the association between notions of women as sex objects and exposure to sexual content of varied explicitness (i.e., sexually non-explicit, semi-explicit, or explicit) and in different formats (i.e., visual and audio-visual) can be better described as cumulative or as hierarchical. Exposure to sexually explicit material in on-line movies was the only exposure measure significantly related to beliefs that women are sex objects in the final regression model, in which exposure to other forms of sexual content was controlled. The relationship between exposure to a sexualized media environment and notions of women as sex objects did not differ for girls and boys

7) The use of cyberpornography by young men in Hong Kong some psychosocial correlates (2007) – Excerpt:

This study examined the prevalence of online pornography viewing and its psychosocial correlates among a sample of young Chinese men in Hong Kong. Moreover, participants who reported to have more online pornography viewing were found to score higher on measures of premarital sexual permissiveness and proclivities toward sexual harassment.

8) X-Rated: Sexual attitudes and behaviors associated with U.S. early adolescents’ exposure to sexually explicit media (2009) – Excerpt:

Correlates of use and subsequent sexual attitudes and behaviors predicted by exposure to sexually explicit content in adult magazines, X-rated movies, and the Internet were examined in a prospective survey of a diverse sample of early adolescents (average age at baseline = 13.6 years; N = 967).

Longitudinal analyses showed that early exposure for males predicted less progressive gender role attitudes, more permissive sexual norms, sexual harassment perpetration, and having oral sex and sexual intercourse two years later. Early exposure for females predicted subsequently less progressive gender role attitudes, and having oral sex and sexual intercourse.

9) Adolescents' Exposure to Sexually Explicit Internet Material and Notions of Women as Sex Objects: Assessing Causality and Underlying Processes (2009) – Excerpt:

The aim of this study was to clarify causality in the previously established link between adolescents’ exposure to sexually explicit Internet material (SEIM) and notions of women as sex objects. On the basis of data from a three-wave panel survey among 962 Dutch adolescents, structural equation modeling initially showed that exposure to SEIM and notions of women as sex objects had a reciprocal direct influence on each other. The direct impact of SEIM on notions of women as sex objects did not vary by gender. However, the direct influence of notions of women as sex objects on exposure to SEIM was only significant for male adolescents. Further analyses showed that, regardless of adolescents’ gender, liking of SEIM mediated the influence of exposure to SEIM on their beliefs that women are sex objects, as well as the impact of these beliefs on exposure to SEIM.

10) Japanese College Students’ Media Exposure to Sexually Explicit Materials, Perceptions of Women, and Sexually Permissive Attitudes (2011) – Excerpt:

The present study examined Japanese college students’ (N  = 476) use of sexually explicit material (SEM) and associations with perceptions of women as sex objects and sexually permissive attitudes. Results indicate that Japanese college students used print media most frequently as a source for SEM followed by the Internet and the television/video/DVD. Male participants used SEM significantly more than females. In addition, sexual preoccupancy mediated the relationship between exposure to SEM and perceptions of women as sex objects, whereas exposure to SEM in mass media had a direct association with Japanese participants’ sexually permissive attitudes.

11) The influence of sexually explicit Internet material and peers on stereotypical beliefs about women’s sexual roles: similarities and differences between adolescents and adults (2011) – Excerpt:

We used data from two nationally representative two-wave panel surveys among 1,445 Dutch adolescents and 833 Dutch adults, focusing on the stereotypical belief that women engage in token resistance to sex (i.e., the notion that women say "no" when they actually intend to have sex). Finally, adults, but not adolescents, were susceptible to the impact of SEIM on beliefs that women engage in token resistance to sex.

12) Pornography Viewing among Fraternity Men: Effects on Bystander Intervention, Rape Myth Acceptance and Behavioral Intent to Commit Sexual Assault (2011) – Excerpt:

The present study surveyed 62% of the fraternity population at a Midwestern public university on their pornography viewing habits, bystander efficacy, and bystander willingness to help in potential rape situations. Results showed that men who view pornography are significantly less likely to intervene as a bystander, report an increased behavioral intent to rape, and are more likely to believe rape myths.

UPDATED SUPPORT:

First, a 2016 review of the literature - Media and Sexualization: State of Empirical Research, 1995–2015 (2016) - Abstract:

Sexually objectifying portrayals of women are a frequent occurrence in mainstream media, raising questions about the potential impact of exposure to this content on others’ impressions of women and on women’s views of themselves. The goal of this review was to synthesize empirical investigations testing effects of media sexualization. The focus was on research published in peer-reviewed, English-language journals between 1995 and 2015. A total of 109 publications that contained 135 studies were reviewed. The findings provided consistent evidence that both laboratory exposure and regular, everyday exposure to this content are directly associated with a range of consequences, including higher levels of body dissatisfaction, greater self-objectification, greater support of sexist beliefs and of adversarial sexual beliefs, and greater tolerance of sexual violence toward women. Moreover, experimental exposure to this content leads both women and men to have a diminished view of women’s competence, morality, and humanity.

Studies published since 2012 that link Internet pornography use to sexist attitudes, objectification, less egalitarian views of women, etc:

1) Pornography and Sexist Attitudes Among Heterosexuals (2013) – Excerpt:

Using a probability-based sample of young Danish adults and a randomized experimental design, this study investigated effects of past pornography consumption, experimental exposure to nonviolent pornography, perceived realism of pornography, and personality (i.e., agreeableness) on sexist attitudes (i.e., attitudes toward women, hostile and benevolent sexism). Further, sexual arousal mediation was assessed. Results showed that, among men, an increased past pornography consumption was significantly associated with less egalitarian attitudes toward women and more hostile sexism. Further, lower agreeableness was found to significantly predict higher sexist attitudes. Significant effects of experimental exposure to pornography were found for hostile sexism among low in agreeableness participants and for benevolent sexism among women.

2) Activating the Centerfold Syndrome: Recency of Exposure, Sexual Explicitness, Past Exposure to Objectifying Media (2013) – Excerpt:

This experimental study tested whether exposure to female centerfold images causes young adult males to believe more strongly in a set of beliefs clinical psychologist Gary Brooks terms “the centerfold syndrome.” The centerfold syndrome consists of five beliefs: voyeurism, sexual reductionism, masculinity validation, trophyism, and nonrelational sex. Past exposure to objectifying media was positively correlated with all five centerfold syndrome beliefs. Recent exposure to centerfolds had immediate strengthening effects on the sexual reductionism, masculinity validation, and nonrelational sex beliefs of males who view objectifying media less frequently. These effects persisted for approximately 48 hours.

3) Pornography Consumption and Opposition to Affirmative Action for Women: A Prospective Study (2013) – Excerpt:

Our study investigated a potential source of social influence that has often been hypothesized to reduce compassion and sympathy for women: pornography. National panel data were employed. Data were gathered in 2006, 2008, and 2010 from 190 adults ranging in age from 19 to 88 at baseline. Pornography viewing was indexed via reported consumption of pornographic movies. Attitudes toward affirmative action were indexed via opposition to hiring and promotion practices that favor women. Consistent with a social learning perspective on media effects, prior pornography viewing predicted subsequent opposition to affirmative action even after controlling for prior affirmative action attitudes and a number of other potential confounds. Gender did not moderate this association. Practically, these results suggest that pornography may be a social influence that undermines support for affirmative action programs for women.

4) Psychological, Relational, and Sexual Correlates of Pornography Use on Young Adult Heterosexual Men in Romantic Relationships (2014) – Excerpt:

The purpose of this study was to examine theorized antecedents (i.e., gender role conflict and attachment styles) and consequences (i.e., poorer relationship quality and sexual satisfaction) of men's pornography use among 373 young adult heterosexual men. Findings revealed that both frequency of pornography use and problematic pornography use were related to greater gender role conflict, more avoidant and anxious attachment styles, poorer relationship quality, and less sexual satisfaction. In addition, the findings provided support for a theorized mediated model in which gender role conflict was linked to relational outcomes both directly and indirectly via attachment styles and pornography use.

5) A National Prospective Study of Pornography Consumption and Gendered Attitudes Toward Women (2015) – Excerpt:

The present study explored associations between pornography consumption and nonsexual gender-role attitudes in a national, two-wave panel sample of US adults. Pornography consumption interacted with age to predict gender-role attitudes. Specifically, pornography consumption at wave one predicted more gendered attitudes at wave two for older—but not for younger—adults.

6) Antecedents of adolescents’ exposure to different types of sexually explicit Internet material: A longitudinal study (2015) - Shows correlation between violent porn use and assessment of hyper-masculine and hyper-feminine attitudes. An excerpt:

The present two-wave panel survey among 1557 Dutch adolescents addressed these lacunae by studying exposure to affection-themed, dominance-themed and violence-themed SEIM. Younger adolescents were more often exposed to affection-themed SEIM, while older adolescents and adolescents with higher levels of academic achievement were more frequently exposed to dominance-themed SEIM. Hyper masculine boys and hyper feminine girls were more frequently exposed to violence-themed SEIM.

7) ‘It’s always just there in your face’: young people’s views on porn (2015) – Excerpt:

Findings highlight that many young people are exposed to porn both intentionally and unintentionally. Furthermore, they are concerned about gendered norms that reinforce men's power and subordination over women. A link between porn exposure, young men's sexual expectations and young women's pressure to conform to what is being viewed, has been exposed.

8) What Is the Attraction? Pornography Use Motives in Relation to Bystander Intervention (2015) – Excerpt:

We found that several motivations to view pornography were associated with suppression of willingness to intervene as a bystander, even after controlling for frequency of pornography use. This study joins others in suggesting an association between pornography use and callousness toward sexual violence.

9) An experimental analysis of young women's attitude toward the male gaze following exposure to centerfold images of varying explicitness (2015) – Women exposed to explicit centerfolds had greater acceptance of men staring at them sexually. An excerpt:

This study measured young women's attitude toward the male gaze following exposure to centerfolds of varying explicitness. Explicitness was operationalized as degree of undress. Women exposed to more explicit centerfolds expressed greater acceptance of the male gaze than women exposed to less explicit centerfolds immediately after exposure and at a 48 hour follow-up. These results support the view that the more media depictions of women display women's bodies, the stronger the message they send that women are sights to be observed by others. They also suggest that even brief exposure to explicit centerfolds can have a nontransitory effect on women's sociosexual attitudes.

10) Men's Objectifying Media Consumption, Objectification of Women, and Attitudes Supportive of Violence Against Women (2016) – Excerpt:

Guided by the concepts of specific and abstract sexual scripting in Wright's sexual script acquisition, activation, application model of sexual media socialization, this study proposed that the more men are exposed to objectifying depictions, the more they will think of women as entities that exist for men's sexual gratification (specific sexual scripting), and that this dehumanized perspective on women may then be used to inform attitudes regarding sexual violence against women (abstract sexual scripting).

Data were gathered from collegiate men sexually attracted to women (N = 187). Consistent with expectations, associations between men's exposure to objectifying media and attitudes supportive of violence against women were mediated by their notions of women as sex objects. Specifically, frequency of exposure to men's lifestyle magazines that objectify women, reality TV programs that objectify women, and pornography predicted more objectified cognitions about women, which, in turn, predicted stronger attitudes supportive of violence against women.

11) Soft-core pornography viewers 'unlikely to hold positive attitudes towards women' (2016) – Excerpt:

Frequent viewers of soft-core pornography, such as photographs of naked and semi-naked female models, are unlikely to think positively about women and are likely to have become desensitised to soft-core pornography common in newspapers, advertising and the media. The results indicated that people who frequently viewed soft-core pornographic images were less likely to describe these as pornographic than people who had low levels of exposure to these images.  People who were desensitised to these images were more likely than others to endorse rape myths. Furthermore, people who frequently viewed these images were less likely to have positive attitudes to women.

12) Pornography, Sexual Coercion and Abuse and Sexting in Young People's Intimate Relationships: A European Study (2016) – Excerpt:

New technology has made pornography increasingly accessible to young people, and a growing evidence base has identified a relationship between viewing pornography and violent or abusive behavior in young men. This article reports findings from a large survey of 4,564 young people aged 14 to 17 in five European countries which illuminate the relationship between regular viewing of online pornography, sexual coercion and abuse and the sending and receiving of sexual images and messages, known as "sexting." In addition to the survey, which was completed in schools, 91 interviews were undertaken with young people who had direct experience of interpersonal violence and abuse in their own relationships.

Rates for regularly viewing online pornography were very much higher among boys and most had chosen to watch pornography. Boys' perpetration of sexual coercion and abuse was significantly associated with regular viewing of online pornography. In addition, boys who regularly watched online pornography were significantly more likely to hold negative gender attitudes. The qualitative interviews illustrated that, although sexting is normalized and perceived positively by most young people, it has the potential to reproduce sexist features of pornography such as control and humiliation.

13) Age of first exposure to pornography shapes men's attitudes toward women (2017) – Excerpt:

Participants (N = 330) were undergraduate men at a large, Midwestern university, ranging in age from 17-54 years (M = 20.65, SD = 3.06). Participants predominantly identified as White (84.9%) and heterosexual (92.6). After providing informed consent, participants completed the study online.

Results indicated that lower age of first exposure to pornography predicted higher adherence to both the Power over Women and the Playboy masculine norms. Additionally, regardless of the nature of the men’s first exposure to pornography (i.e., intentional, accidental, or forced), participants adhered equally to the Power over Women and the Playboy masculine norm. Various explanations may exist to understand these relationships, but the results show the importance of discussing age of exposure in clinical settings with men.

What about this recent anomalous study -"Is Pornography Really about "Making Hate to Women"? Pornography Users Hold More Gender Egalitarian Attitudes Than Nonusers in a Representative American Sample"? It has been heavily cited as strong evidence that porn use leads to greater egalitarianism and less sexist attitudes. Actually, this Taylor Kohut study (like a second 2016 Kohut paper) provides an instructive example of how to twist methodology to achieve a desired result. Namely, that porn use is only beneficial. The authors of this study framed egalitarianism as support for the following: Feminist identification, Women holding positions of power, Women working outside home, and Abortion. Secular populations, which tend to be more liberal, have far higher rates of porn use than religious populations. By choosing these criteria and ignoring endless other relevant variables, lead author Kohut knew he would end up with porn users scoring higher on his study’s carefully chosen selection of what constitutes “egalitarianism.” Then he chose a title that spun it all.


SLIDE 11

Which brings us to a second problem: researchers haven't asked porn users about the kinds of symptoms Zimbardo described in The Demise of Guys [TED talk]. “Arousal addiction" symptoms are easily mistaken for other conditions, such as: ADHD, social anxiety, depression, performance anxiety, OCD, and so on. Healthcare providers assume these conditions are primary - perhaps the cause of addiction, but never the result of addiction. As a consequence, they medicate these guys without inquiring about the possibility of Internet addiction. So, many guys never realize that they could reverse their symptoms by changing their behavior.

ORIGINAL SUPPORT:

"Arousal addiction" (internet addiction and its subtypes):

Zimbardo defined "arousal addiction" as addiction to novelty, as opposed to substance addiction, which is an addiction to more of the same. Zimbardo was referring to "Internet addiction" focusing on its two main subtypes, pornography and video games. Since The Great Porn Experiment was a direct response to Philip Zimbardo's "Demise of Guys" TED talk, I employed the same terminology as Zimbardo (“arousal addiction“) to describe compulsive internet use (video gaming, viewing porn) by young men. In Slide 20, I provided 10 internet-addiction "brain studies" to support the existence of internet addiction and its subtypes. However, already by 2011 (when I prepared my talk), many more psychological studies existed supporting the existence of internet addiction.

"Arousal addiction" exacerbating or causing symptoms (ADHD, social anxiety, anxiety, depression, etc.):

This claim was in large part supported by the thousands of young porn users who reported various symptoms and conditions abating after eliminating porn. Many such accounts appear on the following pages:

The claim that "arousal addiction" can cause or exacerbate mental/emotional problems was also supported by the many published studies already linking internet use (pornography, video gaming) to emotional and cognitive problems. Note: A Google Scholar search for the years 1990-2011 returns nearly 16,000 citations for "internet addiction" + psychiatric symptoms. See Studies published prior to The Great Porn Experiment that reported links between porn use and poorer mental and emotional health. Here are some of them:

1) Variations in internet-related problems and psychosocial functioning in online sexual activities: implications for social and sexual development of young adults (2004) - Excerpts:

Students who did not participate in either online sexual activity were more satisfied with their offline life and more connected to friends and family. Those who engaged in both online sexual activities were more dependent on the Internet and reported lower offline functioning. Despite students' common participation in online sexual activities (OSA) as a venue for social and sexual development, those relying on the Internet and the affiliations it provides appear at risk of decreased social integration.

2) Internet Pornography and Loneliness: An Association? (2005) - Excerpt:

Results showed a significant association between Internet pornography usage and loneliness as evidenced by the data analysis.

3) Use of Internet Pornography and Men's Well-Being (2005) - Excerpt:

Although most individuals utilize the Internet for occupational, educational, recreational, and shopping purposes, a sizable male minority exists, known as Cybersex compulsives and at-risk users, who invest an inordinate amount of their time, money, and energy in the pursuit of Cybersex experiences with negative intrapersonal ramifications in terms of depression, anxiety, and problems with felt intimacy with their real-life partners.

4) Adolescent pornographic internet site use: a multivariate regression analysis of the predictive factors of use and psychosocial implications (2009) - Excerpt:

Compared to non-pornographic Internet site users, infrequent pornographic Internet site users were twice as likely to have abnormal conduct problems; frequent pornographic Internet site users were significantly more likely to have abnormal conduct problems. Thus, both infrequent and frequent pornographic Internet site use are prevalent and significantly associated with social maladjustment among Greek adolescents.

5) Social bonds and Internet pornographic exposure among adolescents (2009) – Summary from a review:

The study found that adolescents with higher degrees of social interaction and bonding were not as likely to consume sexually explicit material as were their less social peers (Mesch, 2009). Additionally, Mesch found that greater quantities of pornography consumption were significantly correlated with lower degrees of social integration, specifically related to religion, school, society, and family. The study also found a statistically significant relationship between pornography consumption and aggressiveness in school....

6)  Frequent users of pornography. A population based epidemiological study of Swedish male adolescents (2010) - Excerpts

Frequent use was also associated with many problem behaviours. High frequent viewing of pornography may be seen as a problematic behaviour that needs more attention from both parents and teachers and also to be addressed in clinical interviews.

7) Mental-and physical-health indicators and sexually explicit media use behavior by adults (2011) - Excerpt:

After adjusting for demographics, Pornography (SEMB) users, compared to nonusers, reported greater depressive symptoms, poorer quality of life, more mental- and physical-health diminished days, and lower health status.

8) Watching Pornographic Pictures on the Internet: Role of Sexual Arousal Ratings and Psychological-Psychiatric Symptoms for Using Internet Sex Sites Excessively (2011) - Scores on a porn addiction questionnaire (IATsex) correlated with higher levels of psychological problems such as: interpersonal sensitivity, depression, paranoid thinking and psychoticism. Excerpts:

We found a positive relationship between subjective sexual arousal when watching Internet pornographic pictures and the self-reported problems in daily life due to the excessiveness of cybersex as measured by the IATsex. Subjective arousal ratings, the global severity of psychological symptoms, and the number of sex applications used were significant predictors of the IATsex score, while the time spent on Internet sex sites did not significantly contribute to explanation of variance in the IATsex score.

In our sample, the global symptom severity (SCL GSI), as well as interpersonal sensitivity, depression, paranoid thinking and psychoticism, were correlated particularly with the IATsex score.

Studies published prior to The Great Porn Experiment that reported links between porn use and poorer cognitive functioning:

1) Is students’ computer use at home related to their mathematical performance at school? (2008) - Excerpt:

Also, students’ cognitive abilities were positively linked to their achievement in mathematics. Finally, watching television had a negative relationship with students’ performance. Particularly, watching horror, action, or pornographic films was associated with lower test scores.

2) Self-reported differences on measures of executive function and hypersexual behavior in a patient and community sample of men (2010) – "Hypersexual behavior" was correlated with poorer executive function (arising primarily from the prefrontal cortex). An excerpt:

Patients seeking help for hypersexual behavior often exhibit features of impulsivity, cognitive rigidity, poor judgment, deficits in emotion regulation, and excessive preoccupation with sex. Some of these characteristics are also common among patients presenting with neurological pathology associated with executive dysfunction. These observations led to the current investigation of differences between a group of hypersexual patients (n = 87) and a non-hypersexual community sample (n = 92) of men using the Behavior Rating Inventory of Executive Function-Adult Version  Hypersexual behavior was positively correlated with global indices of executive dysfunction and several subscales of the BRIEF-A. These findings provide preliminary evidence supporting the hypothesis that executive dysfunction may be implicated in hypersexual behavior.

UPDATED SUPPORT:

"Arousal addiction" (internet addiction and its subtypes):

In support of his TED talk Dr. Philip Zimbardo published two books (each with hundreds of citations):

Studies supporting the existence of Internet addiction and its subtypes (gaming, social media, pornography):

Two recent reviews of the literature (with hundreds of citations) argue for diagnostic categories for internet addiction subtypes (gaming, social media, pornography):

The World Health Organization's next edition of its diagnostic manual, the ICD, is due out in 2018. In alignment with the preponderance of the evidence the new ICD-11 proposes a diagnosis for “Compulsive Sexual Behavior Disorder,” as well as one for “Disorders due to addictive behaviors.” The ICD-11 is also slated to include "Gaming Disorder" (‘digital gaming’ or ‘video-gaming’), which may be online (i.e., over the internet) or offline. Another "arousal addiction," gambling addiction, is already in the DSM.

Part 1(a) - "Arousal addiction" exacerbating or causing symptoms (ADHD, social anxiety, anxiety, depression, etc.). Studies published after The Great Porn Experiment that report links between porn use and poorer mental and emotional health:

1) When is Online Pornography Viewing Problematic Among College Males? Examining the Moderating Role of Experiential Avoidance (2012) - Excerpt:

The current study examined the relationship of Internet pornography viewing and experiential avoidance to a range of psychosocial problems (depression, anxiety, stress, social functioning, and problems related to viewing) through a cross-sectional online survey conducted with a non-clinical sample of 157 undergraduate college males. Results indicated that frequency of viewing was significantly related to each psychosocial variable, such that more viewing was related to greater problems.

2) Women, Female Sex and Love Addicts, and Use of the Internet (2012) - This study compared female cybersex addicts to female sex addicts, and female non-addicts. The cybersex addicts experienced higher levels of depression. An excerpt:

For each of these variables, the pattern was that participants in the cybersex group and participants in the addicted/no cybersex group were more likely to experience depression, attempt suicide, or have withdrawal symptoms than participants in the non-addicted/no cybersex group. Participants in the cybersex group were more likely to report being depressed than participants in the addicted/no cybersex group.

3) Consumption of Pornographic Materials among Hong Kong Early Adolescents: A Replication (2012) - Excerpts:

In general, higher levels of positive youth development and better family functioning were related to a lower level of pornography consumption. The relative contribution of positive youth development and family factors to consumption of pornographic materials was also explored.

The present study attempted to explore the linkage between family functioning and pornography consumption. Three features of family functioning, mutuality, communication and harmony were negatively related to pornography consumption.

4) Emerging Adult Sexual Attitudes and Behaviors: Does Shyness Matter? (2013) - Excerpt:

Shyness was positively associated with solitary sexual behaviors of masturbation and pornography use for men.

5) Narcissism & Internet Pornography Use (2014) - Excerpt:

The hours spent viewing Internet pornography use was positively correlated to participant's narcissism level. Additionally, those who have ever used Internet pornography endorsed higher levels of all three measures of narcissism than those who have never used Internet pornography.

6) Pornography and Marriage (2014) - Porn use correlated with less overall happiness. An excerpt:

We found that adults who had watched an X-rated movie in the past year were more likely to be divorced, more likely to have had an extramarital affair, and less likely to report being happy with their marriage or happy overall. We also found that, for men, pornography use reduced the positive relationship between frequency of sex and happiness.

7) Pornography consumption, psychosomatic health and depressive symptoms among Swedish adolescents (2014) - Excerpts:

The aims of the study were to investigate predictors for frequent use of pornography and to investigate such use in relation to psychosomatic and depressive symptoms among Swedish adolescents. .....we found that being a girl, living with separated parents, attending a vocational high school program, and being a frequent user of pornography at baseline had major effects on psychosomatic symptoms at follow-up.

Frequent use of pornography at baseline predicted psychosomatic symptoms at follow-up to a higher extent compared to depressive symptoms.

8) Use of Pornography and its Associations with Sexual Experiences, Lifestyles and Health among Adolescents (2014) - Excerpts:

In the longitudinal analyses frequent use of pornography was more associated to psychosomatic symptoms compared with depressive symptoms. Male frequent users of pornography more often reported peer-relationship problems than their peers.

9) Psychological, Relational, and Sexual Correlates of Pornography Use on Young Adult Heterosexual Men in Romantic Relationships (2014) - Higher porn use and problematic porn use was linked to more avoidant and anxious attachment styles. Excerpt:

Thus, the purpose of this study was to examine theorized antecedents (i.e., gender role conflict and attachment styles) and consequences (i.e., poorer relationship quality and sexual satisfaction) of men's pornography use among 373 young adult heterosexual men. Findings revealed that both frequency of pornography use and problematic pornography use were related to greater gender role conflict, more avoidant and anxious attachment styles, poorer relationship quality, and less sexual satisfaction.

10) Neural Correlates of Sexual Cue Reactivity in Individuals with and without Compulsive Sexual Behaviours (2014) - Even though Voon et al., 2014 excluded individuals with major psychiatric conditions, the porn addicted subjects scores higher on depression and anxiety assessments. Excerpt:

CSB subjects [porn addicts] had higher depression and anxiety scores (Table S2 in File S1) but no current diagnoses of major depression

11) No Harm in Looking, Right? Men’s Pornography Consumption, Body Image, and Well-Being (2014) - Excerpt:

Path analyses revealed that men’s frequency of pornography use was (a) positively linked to muscularity and body fat dissatisfaction indirectly through internalization of the mesomorphic ideal, (b) negatively linked to body appreciation directly and indirectly through body monitoring, (c) positively linked to negative affect indirectly through romantic attachment anxiety and avoidance, and (d) negatively linked to positive affect indirectly through relationship attachment anxiety and avoidance.

12) Patient Characteristics by Type of Hypersexuality Referral: A Quantitative Chart Review of 115 Consecutive Male Cases (2015) - Study placed "hypersexuals" into 2 categories: "chronic adulterers" and "avoidant masturbators" (who were chronic porn users).

The avoidant masturbator subtype was operationalized as those cases who reported more than 1 hr (or one episode) of masturbation per day or more than 1 hr of pornography viewing per day, or more than 7 hr (or episodes) per week.

With respect to the mental health and sexological variables, the avoidant masturbator subtype [compulsive porn users] was significantly more likely to report a history of anxiety problems and of sexual functioning problems (71% vs. 31%) with delayed ejaculation being the most commonly reported sexual functioning problem.

13) Perceived Addiction to Internet Pornography and Psychological Distress: Examining Relationships Concurrently and Over Time (2015) - Ignore the phrase "perceived addiction, as it really means the total score on the Grubbs's CPUI-9, which is an actual porn addiction questionnaire (see YBOP full critique of the perceived porn addiction concept). Put simply, porn addiction is correlated with psychological distress (anger, depression, anxiety, stress). An excerpt:

At the outset of this study, we hypothesized that "perceived addiction" to Internet pornography would be positively associated with psychological distress. Using a large cross-sectional sample of adult web users and a large cross-sectional sample of undergraduate web users, we found consistent support for this hypothesis. Additionally, in a 1-year longitudinal analysis of undergraduate pornography users, we found links between perceived addiction and psychological distress over time. Collectively, these findings strongly underscore the claim that "perceived addiction" to Internet pornography likely contributes to the experience of psychological distress for some individuals.

14) An Online Assessment of Personality, Psychological, and Sexuality Trait Variables Associated with Self-Reported Hypersexual Behavior (2015) - Porn/sex addiction was not only related to fear of experiencing erectile dysfunction, it was also linked to depression and anxiety. An excerpt:

Hypersexual" behavior represents a perceived inability to control one's sexual behavior. To investigate hypersexual behavior, an international sample of 510 self-identified heterosexual, bisexual, and homosexual men and women completed an anonymous online self-report questionnaire battery. In addition to age and sex (male), hypersexual behavior was related to higher scores on measures of sexual excitation, sexual inhibition due to the threat of performance failure, trait impulsivity, and both depressed mood and anxiety.

15) Lower Psychological Well-Being and Excessive Sexual Interest Predict Symptoms of Compulsive Use of Sexually Explicit Internet Material Among Adolescent Boys (2015) - Excerpt:

This study investigated whether factors from three distinct psychosocial domains (i.e., psychological well-being, sexual interests/behaviors, and impulsive-psychopathic personality) predicted symptoms of compulsive use of sexually explicit Internet material among adolescent boys. Longitudinally, higher levels of depressive feelings and, again, excessive sexual interest predicted relative increases in compulsive use symptoms 6 months later.

16) Psychological, Relational, and Biological Correlates of Ego-Dystonic Masturbation in a Clinical Setting (2016) - The original paper (here) used the phrase "Compulsive Masturbation" to describe the subjects' activity. The paper's publisher (Sexual Medicine Open) changed "Compulsive Masturbation" to "Ego-Dystonic Masturbation." In 2016, compulsive masturbation, in a clinical setting, is synonymous with compulsive porn use. An excerpt:

Our data confirm previous observations that psychiatric comorbidities, especially mood, anxiety, and personality disorders, are the rule rather the exception for people with compulsive sexual behaviors. 21, 22, 23, 24 However, EM could be associated with a non-specific anxious activation.

17) Men’s pornography consumption in the UK: prevalence and associated problem behaviour (2016) - Excerpt:

Those who reported pornography addiction were much more likely to engage in a variety of risky antisocial behaviours, including heavy drinking, fighting, and weapon use, using illegal drugs gambling and viewing illegal images to name but a few. They also reported poorer physical and psychological health.

18) Mood changes after watching pornography on the Internet are linked to symptoms of Internet-pornography-viewing disorder (2016) - Excerpt:

Internet-pornography-viewing disorder (IPD) is considered one type of Internet-use disorder. For IPD's development, it was assumed theoretically that a dysfunctional use of Internet pornography to cope with depressive mood or stress might be considered as a risk factor. Data showed that tendencies towards IPD were associated negatively with feeling generally good, awake, and calm and positively with perceived stress in daily life and using Internet pornography for excitation seeking and emotional avoidance. Moreover, tendencies towards IPD were negatively related to mood before and after Internet-pornography use.

19) Problematic sexual behavior in young adults: Associations across clinical, behavioral, and neurocognitive variables (2016) - Individuals with Problematic Sexual Behaviors (PSB) exhibited several neuro-cognitive deficits and psychological problems. A few excerpts:

This analysis also indicated that PSB was associated with worse quality of life, lower self-esteem, and higher rates of comorbidities across several disorders. Furthermore, the PSB group showed deficits across several neurocognitive domains, including motor inhibition, spatial working memory, and an aspect of decision making. Thus, it is possible that PSB gives rise to a host of secondary problems, ranging from alcohol dependence and depression to deteriorations in quality of life and self-esteem.

20) Problematic internet pornography use: The role of craving, desire thinking, and metacognition (2017) - While not so clear in the text, this study found correlations between cravings for pornography and scores on depression & anxiety questionnaires (negative affect). An excerpt:

The present study tested the metacognitive model of desire thinking and craving for problematic pornography use, and expanded upon the same model to include negative affect related to desire thinking.

21) Effect of internet on the psychosomatic health of adolescent school children in Rourkela - A cross-sectional study (2017) - Excerpts:

Visiting porn sites were associated with interest in sex, low mood, lack of concentration, and unexplained anxiety.

Pornography was significantly associated with several psychological problems in adolescents. Due to the structural immaturity of the adolescent brain and relative inexperience, they are unable to process the myriad nature of sexual content online which may lead to attention problems, anxiety, and depression.

22) Pornography Use and Loneliness: A Bi-Directional Recursive Model and Pilot Investigation (2017) - Excerpt:

Theoretically and empirically, we examine loneliness as it relates to pornography use in terms of pornography's relational scripting and its addictive potential. Results from our analyses revealed significant and positive associations between pornography use and loneliness for all three models. Findings provide grounds for possible future bidirectional, recursive modeling of the relation between pornography use and loneliness.

23) How Abstinence Affects Preferences (2016) [preliminary results] – Excerpts from the article:

Results of the First Wave - Main Findings

  1. The length of the longest streak participants performed before taking part in the survey correlates with time preferences. The second survey will answer the question if longer periods of abstinence render participants more able to delay rewards, or if more patient participants are more likely to perform longer streaks.
  2. Longer periods of abstinence most likely cause less risk aversion (which is good). The second survey will provide the final proof.
  3. Personality correlates with length of streaks. The second wave will reveal if abstinence influences personality or if personality can explain variation in the length of streaks.

Results of the Second Wave - Main Findings

  1. Abstaining from pornography and masturbation increases the ability to delay rewards
  2. Participating in a period of abstinence renders people more willing to take risks
  3. Abstinence renders people more altruistic
  4. Abstinence renders people more extroverted, more conscientious, and less neurotic

24) Viewing Sexually Explicit Media and Its Association with Mental Health Among Gay and Bisexual Men Across the U.S. (2017) - Excerpts

Gay and bisexual men (GBM) have reported viewing significantly more sexually explicit media (SEM) than heterosexual men. There is evidence that viewing greater amounts of SEM may result in more negative body attitude and negative affect. However, no studies have examined these variables within the same model. 

Greater consumption of SEM was directly related to more negative body attitude and both depressive and anxious symptomology. There was also a significant indirect effect of SEM consumption on depressive and anxious symptomology through body attitude. These findings highlight the relevance of both SEM on body image and negative affect along with the role body image plays in anxiety and depression outcomes for GBM.

25) Pornography use in sexual minority males: Associations with body dissatisfaction, eating disorder symptoms, thoughts about using anabolic steroids and quality of life (2017) - Excerpts:

A sample of 2733 sexual minority males living in Australia and New Zealand completed an online survey that contained measures of pornography use, body dissatisfaction, eating disorder symptoms, thoughts about using anabolic steroids and quality of life.

Almost all (98.2%) participants reported pornography use with a median use of 5.33 hours per month. Multivariate analyses revealed that increased pornography use was associated with greater dissatisfaction with muscularity, body fat and height; greater eating disorder symptoms; more frequent thoughts about using anabolic steroids; and lower quality of life.

26) Young Australians' use of pornography and associations with sexual risk behaviours (2017) - Excerpt:

Younger age at first pornography viewing was associated with ... recent mental health problems.

Part 1(b) - Studies published after "The Great Porn Experiment" that reported links between porn use and poorer cognitive functioning:

1) Pornographic picture processing interferes with working memory performance (2013) - German scientists have discovered that Internet erotica can diminish working memory. In this porn-imagery experiment, 28 healthy individuals performed working-memory tasks using 4 different sets of pictures, one of which was pornographic. Participants also rated the pornographic pictures with respect to sexual arousal and masturbation urges prior to, and after, pornographic picture presentation. Results showed that working memory was worst during the porn viewing and that greater arousal augmented the drop. An excerpt:

Results contribute to the view that indicators of sexual arousal due to pornographic picture processing interfere with working memory performance. Findings are discussed with respect to Internet sex addiction because working memory interference by addiction-related cues is well known from substance dependencies.

2) Sexual Picture Processing Interferes with Decision-Making Under Ambiguity (2013) - Study found that viewing pornographic imagery interfered with decision making during a standardized cognitive test. This suggests porn use might affect executive functioning, which is a set of mental skills that help with meeting goals. These skills are controlled by an area of the brain called the prefrontal cortex.

Decision-making performance was worse when sexual pictures were associated with disadvantageous card decks compared to performance when the sexual pictures were linked to the advantageous decks. Subjective sexual arousal moderated the relationship between task condition and decision-making performance. This study emphasized that sexual arousal interfered with decision-making, which may explain why some individuals experience negative consequences in the context of cybersex use.

3) Arousal, working memory capacity, and sexual decision-making in men (2014) - Excerpts:

This study investigated whether working memory capacity (WMC) moderated the relationship between physiological arousal and sexual decision making. A total of 59 men viewed 20 consensual and 20 non-consensual images of heterosexual interaction while their physiological arousal levels were recorded using skin conductance response. Participants also completed an assessment of WMC and a date-rape analogue task for which they had to identify the point at which an average Australian male would cease all sexual advances in response to verbal and/or physical resistance from a female partner. Participants who were more physiologically aroused by and spent more time viewing the non-consensual sexual imagery nominated significantly later stopping points on the date-rape analogue task. Consistent with our predictions, the relationship between physiological arousal and nominated stopping point was strongest for participants with lower levels of WMC. For participants with high WMC, physiological arousal was unrelated to nominated stopping point. Thus, executive functioning ability (and WMC in particular) appears to play an important role in moderating men’s decision making with regard to sexually aggressive behavior.

4) Getting stuck with pornography? Overuse or neglect of cybersex cues in a multitasking situation is related to symptoms of cybersex addiction (2015) - Subjects with a higher tendency towards porn addiction performed more poorly of executive functioning tasks (which are under the auspices of the prefrontal cortex). A few excerpts: 

We investigated whether a tendency towards cybersex addiction is associated with problems in exerting cognitive control over a multitasking situation that involves pornographic pictures. We used a multitasking paradigm in which the participants had the explicit goal to work to equal amounts on neutral and pornographic material. We found that participants who reported tendencies towards cybersex addiction deviated stronger from this goal.

The results of the current study point towards a role of executive control functions, i.e. functions mediated by the prefrontal cortex, for the development and maintenance of problematic cybersex use (as suggested by Brand et al., 2014). Particularly a reduced ability to monitor consumption and to switch between pornographic material and other contents in a goal adequate manner may be one mechanism in the development and maintenance of cybersex addiction

5) Problematic sexual behavior in young adults: Associations across clinical, behavioral, and neurocognitive variables (2016) - Individuals with Problematic Sexual Behaviors (PSB) exhibited several neuro-cognitive deficits. These findings indicate poorer executive functioning (hypofrontality) which is a key brain feature occurring in drug addicts. Excerpts:

From this characterization, it is be possible to trace the problems evident in PSB and additional clinical features, such as emotional dysregulation, to particular cognitive deficits…. If the cognitive problems identified in this analysis are actually the core feature of PSB, this may have notable clinical implications.

6) Effects of Pornography on Senior High School Students, Ghana. (2016) - Excerpt:

The study revealed that majority of the students admitted to watching pornography before. Furthermore, it was observed that majority of them agreed that pornography affects students’ academic performance negatively...

7) Executive Functioning of Sexually Compulsive and Non-Sexually Compulsive Men Before and After Watching an Erotic Video (2017) - Exposure to porn affected executive functioning in men with "compulsive sexual behaviors," but not healthy controls. Poorer executive functioning when exposed to addiction-related cues is a hallmark of substance disorders (indicating both altered prefrontal circuits and sensitization). Excerpts:

This finding indicates better cognitive flexibility after sexual stimulation by controls compared with sexually compulsive participants. These data support the idea that sexually compulsive men do not to take advantage of the possible learning effect from experience, which could result in better behavior modification. This also could be understood as a lack of a learning effect by the sexually compulsive group when they were sexually stimulated, similar to what happens in the cycle of sexual addiction, which starts with an increasing amount of sexual cognition, followed by the activation of sexual scripts and then orgasm, very often involving exposure to risky situations.

8) Exposure to Sexual Stimuli Induces Greater Discounting Leading to Increased Involvement in Cyber Delinquency Among Men (2017) - In two studies exposure to visual sexual stimuli resulted in: 1) greater delayed discounting (inability to delay gratification), 2) greater inclination to engage in cyber-delinquency, 3) greater inclination to purchase counterfeit goods and hack someone's Facebook account. Taken together this indicates that porn use increases impulsivity and may reduce certain executive functions (self-control, judgment, foreseeing consequences, impulse control). Excerpt:

These findings provide insight into a strategy for reducing men's involvement in cyber delinquency; that is, through less exposure to sexual stimuli and promotion of delayed gratification. The current results suggest that the high availability of sexual stimuli in cyberspace may be more closely associated with men's cyber-delinquent behavior than previously thought.

Finally for this section, Psychiatrist Victoria Dunckley has reported dramatic improvements in her young patients who take a hiatus from interactive devices.

Part 2 - "Arousal addiction" exacerbating or causing symptoms (ADHD, social anxiety, anxiety, depression, performance anxiety, etc.). Studies demonstrating that internet use appeared to cause mental, cognitive, or emotional problems.

While most of the preceding studies are correlational, the following studies involve various methodologies that suggest or confirm causation.

A) Pornography studies demonstrating causation:

Here are a handful of Internet pornography studies where porn users eliminated porn use and described outcomes. Abstaining from porn to ascertain its effects is the core concept in my TEDx talk, and in this peer-reviewed paper I wrote in 2016: Eliminate Chronic Internet Pornography Use to Reveal Its Effects. Here are the studies that I know of where porn users attempted to abstain from porn. All of them reported significant results. Five of the eight studies had compulsive porn users with severe sexual dysfunctions abstain from porn. Those 5 studies demonstrate causation as patients healed chronic sexual dysfunctions by removing a single variable (pornography):

  1. Male masturbation habits and sexual dysfunctions (2016)
  2. Is Internet Pornography Causing Sexual Dysfunctions? A Review with Clinical Reports (2016)
  3. Unusual masturbatory practice as an etiological factor in the diagnosis and treatment of sexual dysfunction in young men (2014)
  4. Situational Psychogenic Anejaculation: A Case Study (2014)
  5. How difficult is it to treat delayed ejaculation within a short-term psychosexual model? A case study comparison (2017)

The other three studies:

6) Trading Later Rewards for Current Pleasure: Pornography Consumption and Delay Discounting (2015) - The more pornography that participants consumed, the less able they were to delay gratification. This unique study also had porn users reduce porn use for 3 weeks. The study found that continued porn use was causally related to greater inability to delay gratification (note that the ability to delay gratification is a function of the prefrontal cortex). Excerpt from the first study (median subject age 20) correlated subjects' pornography use with their scores on a delayed gratification task:

"The more pornography that participants consumed, the more they saw the future rewards as worth less than the immediate rewards, even though the future rewards were objectively worth more."

A second study (median age 19) was performed to assess if porn use causes delayed discounting, or the inability to delay gratification. Researchers divided current porn users into two groups:

  1. One group abstained from porn use for 3 weeks,
  2. A second group abstained from their favorite food for 3 weeks.

All participants were told the study was about self-control, and they were randomly chosen to abstain from their assigned activity. The clever part was that the researchers had the second group of porn users abstain from eating their favorite food. This ensured that 1) all subjects engaged in a self-control task, and 2) the second group's porn use was unaffected. At the end of the 3 weeks, participants were involved in a task to assess delay discounting. Important note: While the "porn abstinence group" viewed significantly less porn than the "favorite food abstainers," most did not completely abstain from porn viewing. Even so, the results:

"As predicted, participants who exerted self-control over their desire to consume pornography chose a higher percentage of larger, later rewards compared to participants who exerted self-control over their food consumption but continued consuming pornography."

The group that cut back on their porn viewing for 3 weeks displayed less delay discounting compared with the group that simply abstained from their favorite food. Put simply, abstaining from internet porn increases porn users' ability to delay gratification. From the study:

Thus, building on the longitudinal findings of Study 1, we demonstrated that continued pornography consumption was causally related to a higher rate of delay discounting. Exercising self-control in the sexual domain had a stronger effect on delay discounting than exercising self-control over another rewarding physical appetite (e.g., eating one’s favorite food).

7) How Abstinence Affects Preferences (2016) [preliminary results] – Excerpts from the article:

Results of the First Wave - Main Findings

  1. The length of the longest streak participants performed before taking part in the survey correlates with time preferences. The second survey will answer the question if longer periods of abstinence render participants more able to delay rewards, or if more patient participants are more likely to perform longer streaks.
  2. Longer periods of abstinence most likely cause less risk aversion (which is good). The second survey will provide the final proof.
  3. Personality correlates with length of streaks. The second wave will reveal if abstinence influences personality or if personality can explain variation in the length of streaks.

Results of the Second Wave - Main Findings

  1. Abstaining from pornography and masturbation increases the ability to delay rewards
  2. Participating in a period of abstinence renders people more willing to take risks
  3. Abstinence renders people more altruistic
  4. Abstinence renders people more extroverted, more conscientious, and less neurotic

8) A Love That Doesn’t Last: Pornography Consumption and Weakened Commitment to One’s Romantic Partner (2012) – The study had subjects try to abstain from porn use for 3 weeks. When the two groups were compared, those who continued using pornography reported lower levels of commitment than those who tried to abstain. Excerpts:

The intervention proved effective at reducing or eliminating pornography consumption for the duration of the three-week study, yet did not deter control participants from continuing their consumption. Our hypothesis was supported as participants in the pornography consumption condition reported a substantial reduction in commitment compared to participants in the abstain from pornography condition.

Also, the effect of continued pornography consumption on commitment cannot be explained by a difference in the depletion of self-regulatory resources from exercising greater self-control, as participants in both conditions abstained from something pleasurable (i.e., pornography or a favorite food).

9) Finally, a rare longitudinal study on porn use in young males and academic performance: Early adolescent boys’ exposure to internet pornography: Relationships to pubertal timing, sensation seeking, and academic performance (2014) - Excerpts:

This two-wave panel study aimed to test an integrative model in early adolescent boys (Mean age = 14.10; N = 325) that (a) explains their exposure to Internet pornography by looking at relationships with pubertal timing and sensation seeking, and (b) explores the potential consequence of their exposure to Internet pornography for their academic performance..... Moreover, an increased use of Internet pornography decreased boys’ academic performance six months later.

B) Internet use studies demonstrating causation:

While hundreds of studies link internet use and internet addiction to psychological and cognitive problems, the following studies strongly suggest internet use can cause mental and emotional disorders:

1) Online communication, compulsive internet use, and psychosocial well-being among adolescents: A longitudinal study (2008) – Longitudinal study. Excerpt: “Instant messenger use and chatting in chat rooms were positively related to compulsive Internet use and depression 6 months later.

2) Effect of Pathological Use of the Internet on Adolescent Mental Health (2010) - A prospective study. Excerpt: “Results suggested that young people who are initially free of mental health problems but use the Internet pathologically could develop depression as a consequence.

3) Precursor or Sequela: Pathological Disorders in People with Internet Addiction Disorder (2011) - The unique aspect in this study is that the research subjects had not used the Internet prior to enrolling in college. The study followed first year university students to ascertain what percentage develop Internet addiction, and what risk factors may be in play. After one year of school a small percentage were classified as Internet addicts. Those who developed Internet addiction were initially higher on the obsessive scale, yet lower on scores for anxiety depression, and hostility. An excerpt:

After developing Internet addiction significantly higher scores were observed for depression, anxiety, hostility, interpersonal sensitivity, and psychoticism, suggesting that these were outcomes of Internet addiction disorder. We cannot find a solid pathological predictor for Internet addiction disorder. Internet addiction disorder may bring some pathological problems to the addicts in some ways.

4) Effects of electroacupuncture combined psycho-intervention on cognitive function and event related potentials P300 and mismatch negativity in patients with internet addiction (2012) - After 40 days of reducing internet use and treatments subjects scored better on cognitive tests, with corresponding EEG changes.

5) P300 change and cognitive behavioral therapy in subjects with Internet addiction disorder: A 3 month follow-up study (2011) – Altered EEG readings (indicating cognitive deficits) returned to normal levels after 3 months of treatments.

6) Internet abusers associate with a depressive state but not a depressive trait (2013) - High-risk Internet abusers exhibited a stronger depressive state but did not show a depressive trait (this means internet use probably caused depression).

7) The exacerbation of depression, hostility, and social anxiety in the course of Internet addiction among adolescents: A prospective study (2014) – Longitudinal study (1 year). Adolescents who became addicted exhibited increased depression and hostility. In contrast, the internet addiction remission group showed decreased depression, hostility, and social anxiety.

8) Health officials and university experts in Swansea have found new evidence that excessive use of the internet can cause mental health problems (2015) Excerpt: “We are now beginning to see the psychological impacts of internet misuse on a group of young people. These effects include them becoming much more impulsive, and unable to produce long term plans, which is concerning.

9) Effects of craving behavioral intervention on neural substrates of cue-induced craving in Internet gaming disorder (2016) – Intervention resulted in reversal of brain changes and reduced symptoms of addiction.

10) Changes of quality of life and cognitive function in individuals with Internet gaming disorder: A 6-month follow-up (2016) – Excerpt:  “The IGD patients had more symptoms of depression and anxiety, higher degrees of impulsiveness and anger/aggression, higher levels of distress, poorer QOL, and impaired response inhibition. After 6 months of treatment, patients with IGD showed significant improvements in the severity of IGD, as well as in QOL, response inhibition, and executive functioning.”

11) Effect of electro-acupuncture combined with psychological intervention on mental symptoms and P50 of auditory evoked potential in patients with internet addiction disorder (2017) – Intervention resulted in normalization of EEG readings and decreased symptoms of somatization, obsession and the mental symptoms of depression or anxiety.

12)  The Facebook Experiment: Quitting Facebook Leads to Higher Levels of Well-Being (2016) –Excerpt: “it was demonstrated that taking a break from Facebook has positive effects on the two dimensions of well-being: our life satisfaction increases and our emotions become more positive.”

13) Electro-acupuncture treatment for internet addiction: Evidence of normalization of impulse control disorder in adolescents (2017) – Intervention resulted in significant decrease impulsiveness and psychological symptoms.

14) The Dark Side of Internet Use: Two Longitudinal Studies of Excessive Internet Use, Depressive Symptoms, School Burnout and Engagement Among Finnish Early and Late Adolescents (2016) – Longitudinal study reported that excessive internet use can be a cause of school burnout that can later spill over to depressive symptoms.

15) Effectiveness of Brief Abstinence for Modifying Problematic Internet Gaming Cognitions and Behaviors (2017) – Excerpt: “Brief voluntary abstinence was successful in reducing hours of gaming, maladaptive gaming cognitions, and IGD symptoms.”

16) Craving Behavior Intervention in Ameliorating College Students' Internet Game Disorder: A Longitudinal Study (2017) – Intervention resulted in a significant decrease in the severity of IGD, which manifested as less depression and a shift of psychological needs from the Internet to real life.

17) Differential physiological changes following internet exposure in higher and lower problematic internet users (2017) – Excerpt: “Individuals who identified themselves as having problematic internet use displayed increases in heart rate and systolic blood pressure, as well as reduced mood and increased state of anxiety, following cessation of the internet session. There were no such changes in individuals with no self-reported PIU. These changes were independent of levels of depression and trait anxiety. These changes after cessation of internet use are similar to those seen in individuals who have ceased using sedative or opiate drugs.

18) Reciprocal Relationship between Internet Addiction and Network-Related Maladaptive Cognition among Chinese College Freshmen: A Longitudinal Cross-Lagged Analysis (2017) – Excerpt: “A short-term longitudinal survey…. The results revealed that IA can significantly predict the generation and development of network-related maladaptive cognition, and that when such maladaptive cognitions have been established, they can further adversely affect the extent of the students’ IA.”

19) Association between childhood and adult attention deficit hyperactivity disorder symptoms in Korean young adults with Internet addiction (2017) - Study suggests that adult-onset ADHD may be related to internet addiction.

20) Montreal researchers find 1st link between shooter games, loss of grey matter in hippocampus (2017) - Participants were all healthy 18- to 30-year-olds with no history of playing video games. Brain scans conducted on the participants before and after showed that first person-shooter games resulted in the loss of hippocampal grey matter.

21) Taking Facebook at face value: why the use of social media may cause mental disorder (2017) – Excerpt: “Is it plausible that a negative effect of Facebook use on mental well-being contributes to development of outright mental disorder? The answer to this question is most likely yes.”

22) Orbitofrontal gray matter deficits as marker of Internet gaming disorder: converging evidence from a cross-sectional and prospective longitudinal design (2017) - Longitudinal study found that internet gaming caused the loss of OFC gray matter in both gaming addicts and subjects who were not gamers.

23) Outcome of the Psychological Intervention Program: Internet Use for Youth (2017) - 157 teenage problematic internet users completed eight weekly sessions. Excerpt: An overwhelming majority of participants were able to manage PIU symptoms... Not only did it addresses the PIU behaviour but also helped in reducing social anxiety and increasing social interaction.

24) Internet Addiction Creates Imbalance in the Brain (2017) - Compared with a control group, internet addicts had elevated levels of gamma aminobutyric acid, or GABA, a neurotransmitter that has been linked with other addictions and psychiatric disorders. After 9 weeks of reduced internet use, and cognitive behavioral therapy, GABA levels "normalized".


SLIDE 12

Third, as a culture, we can’t believe that sexual activity could lead to addiction--because "sex is healthy." But today's Internet porn is not sex. It’s as different from real sex as "World Of Warcraft" is from checkers. Watching a screen full of naked body parts won’t magically protect a guy from arousal addiction. On the contrary, this Dutch study found that--of all online activities--porn has the most potential to become addictive.

ORIGINAL SUPPORT:

Note: Slides 3, 4, 5, 6 and 8 provide support for the claim that internet pornography (via tube sites) is qualitatively different from porn of the past.

The study cited in the slide supports the claim that internet porn has the highest potential to be addictive: Predicting Compulsive Internet Use: It's All About Sex! (2006) - An excerpt from this longitudinal study:

The objective of this research was to assess the predictive power of various Internet applications on the development of compulsive Internet use (CIU). The study has a two-wave longitudinal design with an interval of 1 year. The first measurement contained 447 adult heavy Internet users who used the Internet at least 16 h per week and had Internet access at home for at least 1 year. For the second measurement, all participants were invited again, of whom 229 responded. By means of an online questionnaire, the respondents were asked about the time spent on various Internet applications and CIU. On a cross-sectional basis, gaming and erotica seem the most important Internet applications related to CIU. On a longitudinal basis, spending a lot of time on erotica predicted an increase in CIU 1 year later. The addictive potential of the different applications varies; erotica appears to have the highest potential.

Other studies in support of this 2011 claim:

1) Cybersex and the E-teen: What Marriage and Family Therapists Should Know (2008) - An excerpt:

Adolescents who use the Internet regularly (the “e-teen”) present a new set of challenges for marriage and family therapists.  Marriage and family therapists cannot ignore the role the Internet plays in adolescent sexual development and its implication for the family. This article will serve as a primer for the marriage and family therapist when presented with adolescents who engage in online sexual behaviors.

2) Adolescents' Exposure to Sexually Explicit Internet Material and Sexual Preoccupancy: A Three-Wave Panel Study (2008) - Exposure to porn increases sexual preoccupancy. An excerpt:

Sexualized media environment may affect adolescents' sexual development beyond traditionally studied variables, such as sexual attitudes and sexual behavior.

The more frequently adolescents used SEIM, the more often they thought about sex, the stronger their interest in sex became, and the more frequently they became distracted because of their thoughts about sex.

3) Adolescents and Internet Sex Addiction (2009) - An excerpt:

Very little thought or research has been directed to the topic of adolescents and sex addiction. Adolescents who use the Internet regularly present a new set of challenges for therapists. This article examines (a) the basic concepts and unique psychological characteristics of the Internet that relates to adolescents’ online sexual behaviors, (b) the etiology of adolescents’ Internet sex addiction, and (c) treatment and prevention when dealing with problematic online sexual behavior in adolescents. It is concluded that therapists cannot ignore the role that the media, particularly the Internet, plays in adolescents’ life and its impact on the family and society.

UPDATED SUPPORT:

Studies including "porn addiction" rates are still quite rare. However, three recent studies assessing male porn users reported addiction rates of 27.6%, 28%, and 19%: 

1) Online sexual activities: An exploratory study of problematic and non-problematic usage patterns in a sample of men (2016) - This Belgian study (Leuven) found that 27.6% of subjects who had used porn in the last 3 months self-assessed their online sexual activities as problematic. An excerpt (OSA’s mean internet pornography):

The proportion of participants who reported experiencing concerns regarding their involvement in OSAs was 27.6% and of these, 33.9% reported that they had already thought to ask for help for OSA use.

2) Clinical Characteristics of Men Interested in Seeking Treatment for Use of Pornography (2016) - A study on men over 18 who had viewed pornography at least once in the last 6 months. The study reported that 28% of men scored at (or above) the cutoff for possible hypersexual disorder.

3) Cybersex Addiction Among College Students: A Prevalence Study (2017) - In a cross-disciplinary survey of students (avg. age 23), 10.3% scored in the clinical range for cybersex addiction (19% of men and 4% of women). It's important to note that this survey did not limit its participants to porn users.

The following studies describe a new type of "sex addiction," namely, young people without serious comorbidities who are addicted only to internet porn (they don't act out with people):

1) A New Generation of Sexual Addiction (2013). Clinicians have begun to see a "new type" of young sex addict who is addicted to internet porn, yet quite distinct from traditional "sex addicts":

In contrast, a “contemporary” form of rapid-onset sexual addiction has emerged with the explosive growth of Internet technology and is distinguished by “3Cs”: chronicity, content, and culture. Of particular concern is early exposure to graphic sexual material that disrupts normal neurochemical, sexual, and social development in youth.

2) Adolescent hypersexuality: Is it a distinct disorder? (2016) - Again, describing a new type of sex addict": young persons who don't have comorbidities or pre-existing psychopathology (as do traditional sex addicts).

Adolescent hypersexuality, and its position within personality dispositions, is the subject of this presentation. The personality dispositions examined were attachment style, temperament, gender, religiosity, and psychopathology. To do so, 311 high school adolescents (184 boys, 127 girls) between the ages 16–18  most of whom (95.8%) were native Israelis. Five possible empirical models were examined, all based on current theory and research on hypersexuality. The fourth model was found to be compatible with the data, indicating that psychopathology and hypersexuality are independent disorders and are not related by a mediating process.

3) The assessment and treatment of adult heterosexual men with self-perceived problematic pornography use: A review (2017) - The following introduction section of a review provides strong support for the claims put forth in Slide 12 and in The Great Porn Experiment:

Burgeoning neurobiological research has called into question the concept of addiction, which has traditionally been associated with the problematic consumption of alcohol and other substances (Love, Laier, Brand, Hatch, & Hajela, 2015). Evidence suggests, however, that various behaviors can also be classified as an addiction because of the common neurobiological mechanisms and motivational processes at play with both substances and addictive behaviors (Grant, Brewer, & Potenza, 2006; Koob & Le Moal, 2008; Robinson & Berridge, 2008). This radical shift in the understanding of addiction has been accompanied by significant implications for clinical and therapeutic assessment and treatment (Love et al., 2015). This is evidenced by the American Psychiatric Association (APA) acknowledging one behavioral addiction, Gambling Disorder, with its own official classification and another, Internet Gaming Disorder, as a ‘Condition for Further Study’ within the DSM 5 (APA, 2013). The APA has not, however, provided researchers and clinicians with an overarching framework for evaluating other emerging and potentially addictive behaviors. One such behavior is compulsive pornography use, which may have the highest addictive potential of all Internet-related behaviors (Griffiths, 2012; Meerkerk, Van Den Eijnden, & Garretsen, 2006).

Problematic pornography consumption, often referred to as ‘porn addiction’ or ‘internet porn addiction’, can be conceptualized as any use of pornography that leads to and/or produces significant negative interpersonal, vocational, or personal consequences for the user (Grubbs, Exline, Pargament, Hook, & Carlisle, 2015; Grubbs, Volk, Exline, & Pargament, 2015). Increasing evidence suggests that excessive and compulsive pornography consumption has similar effects to substance-dependencies, including interference with working memory performance (Laier, Schulte, & Brand, 2013), neuroplastic changes that reinforce use (Hilton, 2013; Love et al., 2015), and the significant negative association between consumption and grey matter volume in the brain (Kühn & Gallinat, 2014). Indeed, brain scan studies have shown that the brains of self-perceived pornography addicts are comparable to individuals with substance dependence in terms of brain activity as monitored by functional magnetic imaging (fMRI) data (Gola et al., 2017; Voon et al., 2014).

Sexual disorders, in general, have been excluded from formal classification in the DSM-5. In 2010, Kafka's proposal for hypersexual disorder (Kafka, 2010), even though a subsequent field trial supported the reliability and validity of criteria for hypersexual disorder (Reid et al., 2012). Much of the current scientific research pertaining to problematic pornography viewing has been conceptualized as sexual addiction (Orzack & Ross, 2000), sexual impulsivity (Mick & Hollander, 2006), sexual compulsivity (Cooper, Putnam, Planchon, & Boies, 1999), or hypersexual behavior (Rinehart & McCabe, 1998), suggesting there may be similarities among the criteria of these other, related classifications. Kraus and colleagues have suggested the adoption of the term Compulsive Sexual Behavior (CSB) to reflect a broader category of problematic sexual behaviors (including pornography use) that incorporates all of the above terms (Kraus, Voon, et al., 2016). Despite similarities, however, literature suggests that problematic pornography use may be distinct and different from other sexual disorders (Duffy, Dawson, & das Nair, 2016). For example, problematic pornography use can differ from general sexual addiction because sexual activity involving human contact may be more anxiety-provoking than the ease of anonymously, privately, and inexpensively consuming pornography online (Short, Wetterneck, Bistricky, Shutter, & Chase, 2016).

Even though problematic pornography use can impact sexual behaviors, create sexual difficulties, and negatively alter attitudes related to sexuality (Cotiga & Dumitrache, 2015), therapists and clinicians are underprepared when it comes to managing problematic pornography use. Individuals who perceive themselves to have problematic use of pornography face a difficult situation in which therapists lack the sufficient training necessary to manage pornography use (Ayres & Haddock, 2009), even though clinicians believe such consumption patterns are worthy of treatment and intervention (Pyle & Bridges, 2012) and clients continue to regularly disclose habitual pornography use in sessions (Ayres & Haddock, 2009). Without an appropriate understanding of the assessment and treatment of problematic pornography use, the possibility for unethical treatment increases since therapist treatment approaches are more likely to be influenced by personal biases and beliefs (Ayres & Haddock, 2009).

Self-perceived problematic pornography use (SPPPU), or self-perceived pornography addiction, has increasingly emerged as a topic in scientific research, despite lacking formal recognition as a disorder and continued disagreements about its definition, or even existence (Duffy et al., 2016). An individual can experience pornography use as problematic for a myriad of reasons. These include personal or moral, social and relationship, time spent viewing, or viewing in inappropriate contexts such as at work (Twohig & Crosby, 2010). Consequently, even though the consumption habits and behaviors may not be inherently problematic, the costs for individuals for whom it is problematic may be significant (Twohig & Crosby, 2010).

SPPPU refers to the extent to which an individual self-identifies as addicted to pornography and feels they are unable to regulate their pornography use. This definition relies on the user's subjective selfperception and experiences when determining the extent to which the pursuit and subsequent consumption of pornography interferes with everyday life (Grubbs, Exline, et al., 2015; Grubbs, Volk, et al., 2015). Many individuals perceiving themselves to suffer from problematic pornography use feel they do not have viable treatment options; otherwise they would seek help (Ross, Månsson, & Daneback, 2012). This is typically because they feel their pornography use is out of control and have experienced failed attempts at either cutting back or quitting (Kraus, Martino, & Potenza, 2016). Of the small percentage of individuals who seek treatment, most indicated treatment was only marginally helpful (Kraus, Martino, et al., 2016). The purpose of this literature review is to gather, synthesize, and analyze the current literature addressing the treatment of SPPPU in adult heterosexual men, with the principle aim of contributing towards recommendations for clinicians, therapists, and future research in the field.


SLIDE 13

 

Here’s why. This ancient brain circuit evolved to drive us toward food, sex and bonding. As a consequence, extreme versions of these natural rewards register as uniquely valuable. That is, we get extra dopamine for high-calorie food and novel hot babes. Too much dopamine can override our natural satiation mechanisms.

ORIGINAL & UPDATED SUPPORT:

The two claims put forth in slide 13:

  1. The reward circuit evolved to drive us toward food, sex and bonding.
  2. Extreme (supernormal) versions of natural rewards can elevate dopamine. The stimulus responsible registers as potentially valuable and thus can override natural satiation mechanisms.

As the 2 claims put forth in Slide 13 are well supported by decades of research and considered to be common knowledge, I created only one section.

Claim #1: This is common knowledge and not in dispute. See this power point slide from The National Institute on Drug Abuse, or this page from The Canadian Institutes of Health Research.

Claim #2: First, phasic dopamine coding for potential value or salience is fully supported in the literature and considered to be a fundamental neuroscience tenet. A Google scholar search for "dopamine signals reward value" returns 59,000 citations. In simple terms, potential reward value is assessed via phasic mesolimbic dopamine (the reward circuit). A few reviews that support this claim:

1) Dopamine invigorates reward seeking by promoting cue-evoked excitation in the nucleus accumbens (2014) – Excerpt:

The dopamine projection from the ventral tegmental area (VTA) to the NAc is an essential component of the neural circuit that promotes reward-seeking behavior (Nicola, 2007). If NAc dopamine function is reduced experimentally, animals are less likely to exert effort to obtain reward (Salamone and Correa, 2012) and often fail to respond to reward-predictive cues (Di Ciano et al., 2001; Yun et al., 2004; Nicola, 2007, 2010; Saunders and Robinson, 2012). These deficits are due to impairment of a specific component of reward seeking: the latency to initiate approach behavior is increased, whereas the speed of approach, the ability to find the goal and perform the necessary operant behavior required to earn reward, and the ability to consume reward are unaffected (Nicola, 2010). Dopamine must promote approach by influencing the activity of NAc neurons, but the nature of this influence remains unclear. Large proportions of NAc neurons are excited or inhibited by reward-predictive cues (Nicola et al., 2004a; Roitman et al., 2005; Ambroggi et al., 2008, 2011; McGinty et al., 2013), and the excitations begin before onset of cued approach behavior and predict the latency to initiate locomotion (McGinty et al., 2013). Therefore, this activity has the characteristics required of a dopamine-dependent signal that promotes cued approach….

In summary, regardless of the specific pharmacological mechanism, our results demonstrate that NAc dopamine promotes reward-seeking behavior by elevating the excitation of NAc neurons to salient environmental stimuli. The magnitude of this excitation sets the latency of the subject to initiate an approach response. Via this mechanism, dopamine regulates both the vigor and probability of cued reward-seeking.

2) Dopamine signals for reward value and risk: basic and recent data (2010) - Excerpt:

Dopamine neurons show phasic activations to external stimuli. The signal reflects reward, physical salience, risk and punishment, in descending order of fractions of responding neurons. Expected reward value is a key decision variable for economic choices. The reward response codes reward value, probability and their summed product, expected value. The neurons code reward value as it differs from prediction, thus fulfilling the basic requirement for a bidirectional prediction error teaching signal postulated by learning theory….

Large proportions of dopamine neurons are also activated by intense, physically salient stimuli. This response is enhanced when the stimuli are novel; it appears to be distinct from the reward value signal. Dopamine neurons show also unspecific activations to non-rewarding stimuli that are possibly due to generalization by similar stimuli and pseudoconditioning by primary rewards. These activations are shorter than reward responses and are often followed by depression of activity. A separate, slower dopamine signal informs about risk, another important decision variable. The prediction error response occurs only with reward; it is scaled by the risk of predicted reward….

Neurophysiological studies reveal phasic dopamine signals that transmit information related predominantly but not exclusively to reward. Although not being entirely homogeneous, the dopamine signal is more restricted and stereotyped than neuronal activity in most other brain structures involved in goal directed behavior.

3) Dopamine in Motivational Control: Rewarding, Aversive, and Alerting (2010) - Excerpt

Midbrain dopamine neurons are well known for their strong responses to rewards and their critical role in positive motivation. It has become increasingly clear, however, that dopamine neurons also transmit signals related to salient but nonrewarding experiences such as aversive and alerting events. Here we review recent advances in understanding the reward and nonreward functions of dopamine. Based on this data, we propose that dopamine neurons come in multiple types that are connected with distinct brain networks and have distinct roles in motivational control. Some dopamine neurons encode motivational value, supporting brain networks for seeking, evaluation, and value learning. Others encode motivational salience, supporting brain networks for orienting, cognition, and general motivation. Both types of dopamine neurons are augmented by an alerting signal involved in rapid detection of potentially important sensory cues. We hypothesize that these dopaminergic pathways for value, salience, and alerting cooperate to support adaptive behavior.

4) The Mysterious Motivational Functions of Mesolimbic Dopamine (2012) - Excerpt:

Nucleus accumbens dopamine (DA) has been implicated in several behavioral functions related to motivation. Yet the specifics of this involvement are complex and at times can be difficult to disentangle. An important consideration in interpreting these findings is the ability to distinguish between diverse aspects of motivational function that are differentially affected by dopaminergic manipulations. Although ventral tegmental neurons have traditionally been labeled “reward” neurons and mesolimbic DA referred to as the “reward” system, this vague generalization is not matched by the specific findings that have been observed. The scientific meaning of the term “reward” is unclear, and its relation to concepts such as reinforcement and motivation is often ill defined. Pharmacological and DA depletion studies demonstrate that mesolimbic DA is critical for some aspects of motivational function, but of little or no importance for others. Some of the motivational functions of mesolimbic DA represent areas of overlap between aspects of motivation and features of motor control, which is consistent with the well known involvement of nucleus accumbens in locomotion and related processes. Furthermore, despite an enormous literature linking mesolimbic DA to aspects of aversive motivation and learning, a literature which goes back several decades (e.g., Salamone et al., 1994), the established tendency has been to emphasize dopaminergic involvement in reward, pleasure, addiction, and reward-related learning, with less consideration of the involvement of mesolimbic DA in aversive processes. The present review will discuss the involvement of mesolimbic DA in diverse aspects of motivation, with an emphasis

5) Dopamine reward prediction error coding (2016) - Excerpt:

Reward prediction errors consist of the differences between received and predicted rewards. They are crucial for basic forms of learning about rewards and make us strive for more rewards—an evolutionary beneficial trait. Most dopamine neurons in the midbrain of humans, monkeys, and rodents signal a reward prediction error; they are activated by more reward than predicted (positive prediction error), remain at baseline activity for fully predicted rewards, and show depressed activity with less reward than predicted (negative prediction error). The dopamine signal increases nonlinearly with reward value and codes formal economic utility. Drugs of addiction generate, hijack, and amplify the dopamine reward signal and induce exaggerated, uncontrolled dopamine effects on neuronal plasticity.

Claim # 2: That supernormal versions of natural rewards elevate phasic dopamine and override satiation mechanisms is well established, as dopamine provides the motivation to pursue a reward. Highly palatable foods (concentrated sugars/fats/salt), video games, and internet porn are recognized as supernormal stimuli (as discussed on Slide 3). First, a few studies exploring internet applications (porn, video games, Facebook) as supernormal stimuli:

1) Neuroscience of Internet Pornography Addiction: A Review and Update (2015) - Excerpt:

Some internet activities, because of their power to deliver unending stimulation (and activation of the reward system), are thought to constitute supernormal stimuli [24], which helps to explain why users whose brains manifest addiction-related changes get caught in their pathological pursuit. Nobel Prize winning scientist Nikolaas Tinbergen [25] posited the idea of “supernormal stimuli,” a phenomenon wherein artificial stimuli can be created that will override an evolutionarily developed genetic response. To illustrate this phenomenon, Tinbergen created artificial bird eggs that were larger and more colorful than actual bird eggs. Surprisingly, the mother birds chose to sit on the more vibrant artificial eggs and abandon their own naturally laid eggs. Similarly, Tinbergen created artificial butterflies with larger and more colorful wings, and male butterflies repeatedly tried to mate with these artificial butterflies in lieu of actual female butterflies. Evolutionary Psychologist Dierdre Barrett took up this concept in her recent book Supernormal Stimuli: How Primal Urges Overran Their Evolutionary Purpose [26]. “Animals encounter supernormal stimuli mostly when experimenters build them. We humans can produce our own.” [4] (p. 4). Barrett’s examples range from candy to pornography and highly salted or unnaturally sweetened junk food to highly engaging interactive video game playing. In short, generalized internet chronic overuse is highly stimulating. It recruits our natural reward system, but potentially activates it at higher levels than the levels of activation our ancestors typically encountered as our brains evolved, making it liable to switch into an addictive mode [27].

2) Measuring Preference for Supernormal Over Natural Rewards: A Two-Dimensional Anticipatory Pleasure Scale (2015) - Excerpt:

Supernormal (SN) stimuli are artificial products that activate reward pathways and approach behavior more so than naturally occurring stimuli for which these systems were intended. Many modern consumer products (e.g., snack foods, alcohol, and pornography) appear to incorporate SN features, leading to excessive consumption, in preference to naturally occurring alternatives. No measure currently exists for the self-report assessment of individual differences or changes in susceptibility to such stimuli. Therefore, an anticipatory pleasure scale was modified to include items that represented both SN and natural (N) classes of rewarding stimuli. Exploratory factor analysis yielded a two-factor solution, and as predicted, N and SN items reliably loaded on separate dimensions. Internal reliability for the two scales was high, ρ =.93 and ρ =.90, respectively. The two-dimensional measure was evaluated via regression using the N and SN scale means as predictors and self-reports of daily consumption of 21 products with SN features as outcomes. As expected, SN pleasure ratings were related to higher SN product consumption, while N pleasure ratings had either negative or neutral associations to consumption of these products. We conclude that the resulting two-dimensional measure is a potentially reliable and valid self-report measure of differential preference for SN stimuli. While further evaluation is needed (e.g., using experimental measures), the proposed scale may play a useful role in the study of both trait- and state-based variation in human susceptibility to SN stimuli.

Processed foods, psychoactive substances, some retail goods, and various social media and gaming products are readily overconsumed, presenting numerous population health challenges (Roberts, van Vught, & Dunbar, 2012). Evolutionary psychology provides a persuasive explanation of excessive consumption. Animals, including humans, tend to approach (i.e., gather, acquire, and consume) stimuli that provide the highest relative reward for their efforts, thereby optimizing their utility (Chakravarthy & Booth, 2004; Kacelnik & Bateson, 1996). Neurological reward mechanisms evolved to promote adaptive behavior by reinforcing stimuli that send signals of promoting fitness, such as providing nutrients or reproductive opportunities. Tinbergen (1948) coined the term “Supernormal Stimulus” upon finding that animals tend to exhibit heightened responses to exaggerated versions of natural stimuli. This “selection asymmetry” (Staddon, 1975; Ward, 2013) is not maladaptive in natural environments in which exaggerated versions of the stimulus are rare—but presents problems when artificial and exaggerated alternatives exist. For example, the newly hatched herring gull prefers to peck at a fabricated thin red rod with white bands at its tip, rather than its mother’s naturally red spotted thin beak (Tinbergen & Perdeck, 1951). In the context of resource selection, the outcome is a behavioral heuristic of “get all you can”: an adaptive strategy in natural environments where resource supply is scarce or unreliable. In the modern human environment, many highly rewarding experiences exist in the form of artificial consumer products that have been designed or refined to be supernormal. That is, they stimulate an evolved reward system to a degree not found in natural stimuli (Barrett, 2010). For example, psychoactive substances (Nesse & Berridge, 1997), commercial fast-food products (Barrett, 2007), gambling products (Rockloff, 2014), television shows (Barrett, 2010; Derrick, Gabriel, & Hugenberg, 2009), digital social networking and the Internet (Rocci, 2013; Ward, 2013), and various retail products, such as expensive cars (Erk, Spitzer, Wunderlich, Galley, & Walter, 2002), high-heeled shoes (Morris, White, Morrison, & Fisher, 2013), cosmetics (Etcoff, Stock, Haley, Vickery, & House, 2011), and children’s toys (Morris, Reddy, & Bunting, 1995) have all been discussed as forms of modern day supernormal stimuli. For some of these stimuli, neurological evidence has shown that they tend to activate dopamine pathways intensely, hijacking the reward response designed for natural rewards, thereby promoting excess consumption and in some cases, addiction (Barrett, 2010; Blumenthal & Gold, 2010; Wang et al., 2001).

To varying degrees, supernormal stimuli tend to be unhealthy. The ready availability of high-calorie takeaway meals and snacks, the toxicity of alcohol and other substances, the sedentary activity involved in watching television, using digital media and gaming products, and the expense of retail items or gambling, all serve to provide an environment that fosters unhealthy behavioral choices, leading to harms (Barrett, 2007, 2010; Birch, 1999; Hantula, 2003; Ward, 2013). This makes the study of susceptibility of modern humans to supernormal stimuli of practical significance. In the current report, we use the term supernormal stimuli to refer to modern human products and experiences that are characterized by asymmetric selectivity (uncontrolled approach to more intense variants) and being made artificially abundant in the modern world. These products are often processed, refined, or synthesized consumer goods including snack foods or substances. Less obvious examples include messages received via social media. Although at times less stimulating than a face-to-face conversation, this communication method provides prolonged enhanced visual, speed, and delivery characteristics. Similarly, most modern day clothing and other retail products exhibit similar enhanced signifiers of rarity or desirability, with attendant implications for sexual or social status. Consumption or acquisition of these products is theorized to provide immediate reward due to being interpreted as fitness enhancing.

It has been suggested a preference for supernormal reward could be the result of differences in dopamine functioning. Dopamine deficiency has been found to be related to various forms of excess consumption including alcohol abuse, binge eating, problem gambling, and Internet addiction (Bergh, Eklund, Södersten, & Nordin, 1997; Blum, Cull, Braverman, & Comings, 1996; Johnson & Kenny, 2010; Kim et al., 2011). The concept of supernormal susceptibility is consistent with an interpretation in terms of individual variability in the dopamine functioning. Dopaminergic pathways, evolved to prioritize resource acquisition and consumption in a resource-scarce environment, are likely to be particularly sensitive to psychoactive substances, energy-dense food, and other modern day consumer products exhibiting exaggerated reward properties (Barrett, 2010; Nesse & Berridge, 1997; Wang et al., 2001). If this is the case, then the two-dimensional NPS/SNPS described here would be expected to discriminate individuals with dopamine dysfunction. Future research might profitably employ neurophysiological techniques in conjunction with self-report measures, in order to confirm the correspondences between these two levels of description.

Supernormal experiences are inherently unhealthy and amenable to excess consumption due to their processed characteristics (e.g., snacks and take away foods) and encouraging prolonged sedentary behavior (e.g., social networking and gaming). Therefore, the ability to identify individuals who prefer these types of reward provides a valuable contribution to those researching, treating, and preventing population health problems caused by over consumption.

3) Pornography addiction – a supranormal stimulus considered in the context of neuroplasticity (2013) - Excerpt:

Addiction has been a divisive term when applied to various compulsive sexual behaviors (CSBs), including obsessive use of pornography. Despite a growing acceptance of the existence of natural or process addictions based on an increased understanding of the function of the mesolimbic dopaminergic reward systems, there has been a reticence to label CSBs as potentially addictive. While pathological gambling (PG) and obesity have received greater attention in functional and behavioral studies, evidence increasingly supports the description of CSBs as an addiction. This evidence is multifaceted and is based on an evolving understanding of the role of the neuronal receptor in addiction-related neuroplasticity, supported by the historical behavioral perspective. This addictive effect may be amplified by the accelerated novelty and the ‘supranormal stimulus’ (a phrase coined by Nikolaas Tinbergen) factor afforded by Internet pornography….

It is surprising that food addiction would not be included as a behavioral addiction, despite studies demonstrating dopaminergic receptor downregulation in obesity (Wang et al., 2001), with reversibility seen with dieting and normalization of body mass index (BMI) (Steele et al., 2010). The concept of a ‘supranormal stimulus’, invoking Nikolaas Tinbergen's term (Tinbergen, 1951), has recently been described in the context of intense sweetness surpassing cocaine reward, which also supports the premise of food addiction (Lenoir, Serre, Laurine, & Ahmed, 2007). Tinbergen originally found that birds, butterflies, and other animals could be duped into preferring artificial substitutes designed specifically to appear more attractive than the animal's normal eggs and mates. There is, of course, a lack of comparable functional and behavioral work in the study of human sexual addiction, as compared to gambling and food addictions, but it can be argued that each of these behaviors can involve supranormal stimuli. Deirdre Barrett (2010) has included pornography as an example of a supranormal stimulus…..

Pornography is a perfect laboratory for this kind of novel learning fused with a powerful pleasure incentive drive. The focused searching and clicking, looking for the perfect masturbatory subject, is an exercise in neuroplastic learning. Indeed, it is illustrative of Tinbergen's concept of the ‘supranormal stimulus’ (Tinbergen, 1951), with plastic surgery–enhanced breasts presented in limitless novelty in humans serving the same purpose as Tinbergen's and Magnus's artificially enhanced female butterfly models; the males of each species prefer the artificial to the naturally evolved (Magnus, 1958; Tinbergen, 1951). In this sense, the enhanced novelty provides, metaphorically speaking, a pheromone-like effect in human males, like moths, which is ‘inhibiting orientation’ and ‘disrupting pre-mating communication between the sexes by permeating the atmosphere’ (Gaston, Shorey, & Saario, 1967)…..

Even public opinion seems to be trying to describe this biologic phenomenon, as in this statement from Naomi Wolf; ‘For the first time in human history, the images’ power and allure have supplanted that of real naked women. Today real naked women are just bad porn’ (Wolf, 2003). Just as Tinbergen's and Magnus's ‘butterfly porn’ successfully competed for male attention at the expense of real females (Magnus, 1958; Tinbergen, 1951), we see this same process occurring in humans.

4) Is Internet Pornography Causing Sexual Dysfunctions? A Review with Clinical Reports (2016) - Excerpt:

3.2. Internet Pornography as Supernormal Stimulus

Arguably, the most important development in the field of problematic sexual behavior is the way in which the Internet is influencing and facilitating compulsive sexual behavior [73]. Unlimited high-definition sexual videos streaming via “tube sites” are now free and widely accessible, 24 h a day via computers, tablets and smartphones, and it has been suggested that Internet pornography constitutes a supernormal stimulus, an exaggerated imitation of something our brains evolved to pursue because of its evolutionary salience [74,75]. Sexually explicit material has been around for a long time, but (1) video pornography is significantly more sexually arousing than other forms of pornography [76,77] or fantasy [78]; (2) novel sexual visuals have been shown to trigger greater arousal, faster ejaculation, and more semen and erection activity compared with familiar material, perhaps because attention to potential novel mates and arousal served reproductive fitness [75,79,80,81,82,83,84]; and (3) the ability to self-select material with ease makes Internet pornography more arousing than pre-selected collections [79]. A pornography user can maintain or heighten sexual arousal by instantly clicking to a novel scene, new video or never encountered genre. A 2015 study assessing Internet pornography’s effects on delay discounting (choosing immediate gratification over delayed rewards of greater value) states, “The constant novelty and primacy of sexual stimuli as particularly strong natural rewards make internet pornography a unique activator of the brain’s reward system. ... It is therefore important to treat pornography as a unique stimulus in reward, impulsivity, and addiction studies” [75] (pp. 1, 10).

Novelty registers as salient, enhances reward value, and has lasting effects on motivation, learning and memory [85]. Like sexual motivation and the rewarding properties of sexual interaction, novelty is compelling because it triggers bursts of dopamine in regions of the brain strongly associated with reward and goal-directed behavior [66]. While compulsive Internet pornography users show stronger preference for novel sexual images than healthy controls, their dACC (dorsal anterior cingulate cortex) also shows more rapid habituation to images than healthy controls [86], fueling the search for more novel sexual images. As co-author Voon explained about her team’s 2015 study on novelty and habituation in compulsive Internet pornography users, “The seemingly endless supply of novel sexual images available online [can feed an] addiction, making it more and more difficult to escape” [87]. Mesolimbic dopamine activity can also be enhanced by additional properties often associated with Internet pornography use such as, violation of expectations, anticipation of reward, and the act of seeking/surfing (as for Internet pornography) [88,89,90,91,92,93]. Anxiety, which has been shown to increase sexual arousal [89,94], may also accompany Internet pornography use. In short, Internet pornography offers all of these qualities, which register as salient, stimulate dopamine bursts, and enhance sexual arousal.

For obvious reasons animal studies on the neurological effects of internet porn and video gaming will never be done. However, numerous animal studies revealing the neurological effects highly palatable foods (concentrated sugars/fats), have been published. Here are a few examples that support the assertion that hyper-palatable food (supernormal stimuli) alters the brain in ways regular diet cannot:

1) Food Addiction (2013) - Excerpts:

Throughout history, people were concerned with eating sufficiently to survive and reproduce. It is only recently with the advent of the modern food industry that the mass consumption of easily accessible high-calorie, tasty foods (e.g., high in sugars and/or fats) has produced an evolutionarily novel state in which many people eat too much and become too fat. In the modern food environment, people report consuming hyperpalatable foods no longer only to get calories but also to experience rewarding sensations, to cope with stress or fatigue, to enhance cognition, and/or to ameliorate mood. Highly processed foods containing high concentrations of refined macronutrients are no longer viewed solely from the angle of energy balance. Some refined ingredients, such as sugars, are progressively more viewed, by laypeople and scientists alike, as addictive substances and their chronic overconsumption as food addiction. Once a controversial concept, food addiction is now considered as serious as other forms of addiction, including cocaine or heroin addiction. The present chapter describes established research, involving both animal models and clinical research, on the neurobiology of sugar addiction. The focus on sugar addiction as a paradigmatic example is all the more important in view of the inexorable “sweetening of the world’s diet.” Much daily gratification that people derive from food consumption comes from the sweet taste of highly sugar-sweetened foods and beverages. In addition, there is growing evidence linking increased sugar availability and consumption, particularly in infants, to the current worldwide obesity epidemic. Despite the focus on sugar addiction, some of the main conclusions drawn can be generalized to other types of food addiction.

2) Intense Sweetness Surpasses Cocaine Reward (2008) - Excerpts:

Refined sugars (e.g., sucrose, fructose) were absent in the diet of most people until very recently in human history. Today overconsumption of diets rich in sugars contributes together with other factors to drive the current obesity epidemic. Overconsumption of sugar-dense foods or beverages is initially motivated by the pleasure of sweet taste and is often compared to drug addiction. Though there are many biological commonalities between sweetened diets and drugs of abuse, the addictive potential of the former relative to the latter is currently unknown.

Our findings clearly demonstrate that intense sweetness can surpass cocaine reward, even in drug-sensitized and -addicted individuals. We speculate that the addictive potential of intense sweetness results from an inborn hypersensitivity to sweet tastants. In most mammals, including rats and humans, sweet receptors evolved in ancestral environments poor in sugars and are thus not adapted to high concentrations of sweet tastants. The supranormal stimulation of these receptors by sugar-rich diets, such as those now widely available in modern societies, would generate a supranormal reward signal in the brain, with the potential to override self-control mechanisms and thus to lead to addiction.

3) Examining the addictive-like properties of binge eating using an animal model of sugar dependence (2007) - Excerpts:

The increase in the incidence of obesity and eating disorders has encouraged research efforts aimed at understanding the etiology of abnormal eating behaviors. Clinical reports have led to the suggestion that some individuals may develop addictive-like behaviors when consuming palatable foods. Binge eating is a behavioral component of bulimia and obesity and has also become increasingly common in nonclinical populations in our society. This review summarizes the behavioral and neurochemical similarities between binge eating of palatable foods and the administration of drugs of abuse. An animal model of bingeing on sugar is used to illustrate behaviors found with some drugs of abuse, such as opiate-like withdrawal signs, enhanced intake following abstinence, and cross-sensitization. Related neurochemical changes commonly observed with drugs of abuse, including changes in dopamine and acetylcholine release in the nucleus accumbens, can also be found with bingeing on sugar.

4) Animal Models of Sugar and Fat Bingeing: Relationship to Food Addiction and Increased Body Weight (2012) - Excerpts:

Binge eating is a behavior that occurs in some eating disorders, as well as in obesity and in nonclinical populations. Both sugars and fats are readily consumed by human beings and are common components of binges. This chapter describes animal models of sugar and fat bingeing, which allow for a detailed analysis of these behaviors and their concomitant physiological effects. The model of sugar bingeing has been used successfully to elicit behavioral and neurochemical signs of dependence in rats; e.g., indices of opiate-like withdrawal, increased intake after abstinence, cross-sensitization with drugs of abuse, and the repeated release of dopamine in the nucleus accumbens following repeated bingeing. Studies using the model of fat bingeing suggest that it can produce some, but not all, of the signs of dependence that are seen with sugar binge eating, as well as increase body weight, potentially leading to obesity.

5) Homeostatic and Hedonic Signals Interact in the Regulation of Food Intake (2009) - Excerpts:

As might be expected, prolonged activation of the limbic system by drugs of abuse leads to cellular and molecular adaptations that serve in part to maintain homeostasis in dopamine signaling (2). Within the dopaminergic neurons of the VTA, chronic drug use is associated with decreased basal dopamine secretion, decreased neuronal size, and increased activity of tyrosine hydroxylase (the rate-limiting enzyme in dopamine biosynthesis) and of the transcription factor cyclic AMP response element binding protein (CREB) (2,10). Within target neurons in the striatum, chronic drug use increases levels of CREB as well as those of another transcription factor, deltaFosB, both of which alter neuronal responsiveness to dopamine signaling (2). These adaptations are thought to be important for the aberrant motivation to obtain drugs of abuse observed in addicted patients. For instance, increasing deltaFosB levels in the striatum increases sensitivity to the rewarding effects of drugs of abuse such as cocaine and morphine and increases incentive motivation to obtain them (2).

Similar cellular and molecular changes have been described in rodents exposed to highly palatable foods. Mice exposed to a high-fat diet for 4 wk and then abruptly withdrawn to a less palatable semipurified diet showed decreased levels of active CREB in the striatum up to 1 wk after the switch (11). These findings are consistent with the work of Barrot et al. (12) who reported that decreasing CREB activity in the ventral striatum increases the preference for both a sucrose solution (a natural reward) and for morphine, a well-characterized drug of abuse. In addition, mice exposed to 4 wk of high-fat diet exhibited a significant elevation in the level of deltaFosB in the nucleus accumbens (11), similar to changes observed following exposure to drugs of abuse (2). Furthermore, increased expression of deltaFosB in this brain region enhances food-reinforced operant responding, demonstrating a clear role for deltaFosB in increasing motivation to obtain food rewards (13). Taken together, these studies demonstrate that limbic regions experience similar neuroadaptations following exposure to both food and drug rewards and that these adaptations alter the motivation to obtain both types of rewards.

6) Adaptations in brain reward circuitry underlie palatable food cravings and anxiety induced by high-fat diet withdrawal (2013) - Excerpts:

Six weeks of HFD resulting in significant weight gain elicited sucrose anhedonia, anxiety-like behaviour and hypothalamic-pituitary-adrenocortical axis (HPA) hypersensitivity to stress. Withdrawal from HFD but not LFD-potentiated anxiety and basal corticosterone levels and enhanced motivation for sucrose and high-fat food rewards. Chronic high-fat feeding reduced CRF-R1 and increased BDNF and pCREB protein levels in the amygdala and reduced TH and increased ΔFosB protein in NAc and VTA. Heightened palatable food reward in mice withdrawn from HFD coincided with increased BDNF protein levels in NAc and decreased TH and pCREB expression in the amygdala.

Anhedonia, anxiety and sensitivity to stressors develops during the course of HFD and may have a key role in a vicious cycle that perpetuates high-fat feeding and the development of obesity. Removal of HFD enhances stress responses and heightens vulnerability for palatable foods by increasing food-motivated behaviour. Lasting changes in dopamine and plasticity-related signals in reward circuitry may promote negative emotional states, overeating and palatable food relapse.

7) ΔFosB-Mediated Alterations in Dopamine Signaling Are Normalized by a Palatable High-Fat Diet (2008) - Excerpts:

Sensitivity to reward has been implicated as a predisposing factor for behaviors related to drug abuse as well as overeating. However, the underlying mechanisms contributing to reward sensitivity are unknown. We hypothesized that a dysregulation in dopamine signaling might be an underlying cause of heightened reward sensitivity whereby rewarding stimuli could act to normalize the system.

We used a genetic mouse model of increased reward sensitivity, the ΔFosB-overexpressing mouse, to examine reward pathway changes in response to a palatable high-fat diet. Markers of reward signaling in these mice were examined both basally and following 6 weeks of palatable diet exposure. Mice were examined in a behavioral test following high-fat diet withdrawal to assess the vulnerability of this model to removal of rewarding stimuli.

Our results demonstrate altered reward pathway activation along the nucleus accumbens-hypothalamic-ventral tegmental area circuitry resulting from overexpression of ΔFosB in the nucleus accumbens and striatal regions. Levels of phosphorylated cyclic adenosine monophosphate (cAMP) response element binding protein (pCREB), brain-derived neurotrophic factor (BDNF), and dopamine and cyclic adenosine monophosphate regulated phosphoprotein with a molecular mass of 32 kDa (DARPP-32) in the nucleus accumbens were reduced in ΔFosB mice, suggestive of reduced dopamine signaling. Six weeks of high-fat diet exposure completely ameliorated these differences, revealing the potent rewarding capacity of a palatable diet. ΔFosB mice also showed a significant increase in locomotor activity and anxiety-related responses 24 hours following high-fat withdrawal.

These results establish an underlying sensitivity to changes in reward related to dysregulation of ΔFosB and dopamine signaling that can be normalized with palatable diets and may be a predisposing phenotype in some forms of obesity.

8) Diet-induced obesity promotes depressive-like behaviour that is associated with neural adaptations in brain reward circuitry (2013) - Excerpts:

To determine the impact of a palatable high-fat diet (HFD) on depressive-like behaviour and biochemical alterations in brain reward circuitry in order to understand the neural processes that may contribute to the development of depression in the context of diet-induced obesity (DIO).

Our results demonstrate that chronic consumption of high-fat food and obesity induce plasticity-related changes in reward circuitry that are associated with a depressive-like phenotype. As increases in striatal BDNF and CREB activity are well implicated in depressive behaviour and reward, we suggest these signalling molecules may mediate the effects of high-fat feeding and DIO to promote negative emotional states and depressive-like symptomology.

The claim that elevated dopamine can function to override natural satiation mechanisms is widely accepted and the basis for the current model of addiction, called the incentive-sensitization theory of addiction. The following reviews describe dopamine's role in increased wanting or craving, and thus overconsumption of drugs and natural rewards:

1) The incentive sensitization theory of addiction: some current issues (2008) - Excerpts:

It is easy to get the impression from the literature that behavioural sensitization might be equivalent to ‘sensitization of locomotor activity’, but locomotion is only one of many different psychomotor effects of drugs that undergo sensitization, most of which are dissociable (Robinson & Becker 1986). It is important to remember that in this context the word sensitization simply refers to an increase in a drug effect caused by repeated drug administration. What is critical for the incentive sensitization theory is not ‘locomotor sensitization’, or even ‘psychomotor sensitization’, but incentive sensitization. Insofar as psychomotor activation is thought to reflect the engagement of brain incentive systems, including mesotelencephalic dopamine systems (Wise & Bozarth 1987), psychomotor sensitization may often be used as evidence (albeit indirect evidence) for hypersensitivity in relevant motivation circuitry. But it is the hypersensitivity in this motivation circuitry, not the locomotion circuitry, which contributes most to addictive wanting for drugs.

2) Addiction: A Disease of Learning and Memory (2007) - Excerpts:

A large body of work, including pharmacological, lesion, transgenic, and microdialysis studies, has established that the rewarding properties of addictive drugs depend on their ability to increase dopamine in synapses made by midbrain ventral tegmental area neurons on the nucleus accumbens (3840), which occupies the ventral striatum, especially within the nucleus accumbens shell region (41). Ventral tegmental area dopamine projections to other forebrain areas such as the prefrontal cortex and amygdala also play a critical role in shaping drug-taking behaviors (42).

Addictive drugs represent diverse chemical families, stimulate or block different initial molecular targets, and have many unrelated actions outside the ventral tegmental area/nucleus accumbens circuit, but through different mechanisms (e.g., see references 43, 44), they all ultimately increase synaptic dopamine within the nucleus accumbens….

Memory disorders are often thought of as conditions involving memory loss, but what if the brain remembers too much or too powerfully records pathological associations? During the last decade, advances in understanding the role of dopamine in reward-related learning (8) have made a compelling case for a “pathological learning” model of addiction that is consistent with long-standing observations about the behavior of addicted people (6). This work, along with more recent computational analyses of dopamine action (9, 10), has suggested mechanisms by which drugs and drug-associated stimuli might attain their motivational power. At the same time, cellular and molecular investigations have revealed similarities between the actions of addictive drugs and normal forms of learning and memory (1114), with the caveat that our current knowledge of how memory is encoded (15) and how it persists (15, 16) is far from complete for any mammalian memory system. Here I argue that addiction represents a pathological usurpation of the neural mechanisms of learning and memory that under normal circumstances serve to shape survival behaviors related to the pursuit of rewards and the cues that predict them (11, 17–20).

3) Dopamine Signaling in reward-related behaviors (2013) - Excerpts:

Dopamine (DA) regulates emotional and motivational behavior through the mesolimbic dopaminergic pathway. Changes in DA mesolimbic neurotransmission have been found to modify behavioral responses to various environmental stimuli associated with reward behaviors. Psychostimulants, drugs of abuse, and natural reward such as food can cause substantial synaptic modifications to the mesolimbic DA system. Recent studies using optogenetics and DREADDs, together with neuron-specific or circuit-specific genetic manipulations have improved our understanding of DA signaling in the reward circuit, and provided a means to identify the neural substrates of complex behaviors such as drug addiction and eating disorders.

Regulation of the DA system in reward-related behaviors has received a great deal of attention because of the serious consequences of dysfunction in this circuit, such as drug addiction and food reward linked obesity, which are both major public health issues. It is now well accepted that following repeated exposure to addictive substances, adaptive changes occur at the molecular and cellular level in the DA mesolimbic pathway, which is responsible for regulating motivational behavior and for the organization of emotional and contextual behaviors (Nestler and Carlezon, 2006; Steketee and Kalivas, 2011). These modifications to the mesolimbic pathway are thought to lead to drug dependence, which is a chronic, relapsing disorder in which compulsive drug-seeking and drug-taking behaviors persist despite serious negative consequences (Thomas et al., 2008).

Considerable evidence now suggests that substantial synaptic modifications of the mesolimbic DA system are associated with not only the rewarding effects of psychostimulants and other drugs of abuse, but also with the rewarding effects of natural reward, such as food; however, the mechanism by which drugs of abuse induce the modify synaptic strength in this circuit remains elusive. In fact, DA reward signaling seems extremely complex, and is also implicated in learning and conditioning processes, as evidenced by studies revealing a DAergic response coding a prediction error in behavioral learning....

4) The Influence of ΔFosB in the Nucleus Accumbens on Natural Reward Related Behavior (2008) - Excerpt:

The transcription factor deltaFosB (ΔFosB), induced in nucleus accumbens (NAc) by chronic exposure to drugs of abuse, has been shown to mediate sensitized responses to these drugs. However, less is known about a role for ΔFosB in regulating responses to natural rewards. Here, we demonstrate that two powerful natural reward behaviors, sucrose drinking and sexual behavior, increase levels of ΔFosB in the NAc. We then use viral-mediated gene transfer to study how such ΔFosB induction influences behavioral responses to these natural rewards. We demonstrate that overexpression of ΔFosB in the NAc increases sucrose intake and promotes aspects of sexual behavior. In addition, we show that animals with previous sexual experience, which exhibit increased ΔFosB levels, also show an increase in sucrose consumption. This work suggests that ΔFosB is not only induced in the NAc by drugs of abuse, but also by natural rewarding stimuli. Additionally, our findings show that chronic exposure to stimuli that induce ΔFosB in the NAc can increase consumption of other natural rewards.

5) Neuroplasticity in the Mesolimbic System Induced by Natural Reward and Subsequent Reward Abstinence. (2010) – Excerpts:

Natural reward and drugs of abuse converge on the mesolimbic system, where drugs of abuse induce neuronal alterations. Here, we tested plasticity in this system after natural reward and the subsequent impact on drug responses.

Sexual experience induces functional and morphological alterations in the mesolimbic system similar to repeated exposure to psychostimulants. Moreover, abstinence from sexual behavior after repeated mating was essential for increased reward for drugs and dendritic arbors of NAc neurons, suggesting that the loss of sexual reward might also contribute to neuroplasticity of the mesolimbic system. These results suggest that some alterations in the mesolimbic system are common for natural and drug reward and might play a role in general reinforcement.

Additional support for the concept that dopamine overrides normal satiation mechanisms in humans comes from studies on patients given dopamine agonists. A few such studies:

1) Dopamine agonist-triggered pathological behaviors: surveillance in the PD clinic reveals high frequencies (2011). Excerpt:

Of 321 PD patients taking an agonist, 69 (22%) experienced compulsive behaviors, and 50/321 (16%) were pathologic. However, when the analysis was restricted to patients taking agonist doses that were at least minimally therapeutic, pathological behaviors were documented in 24%. The subtypes were: gambling (25; 36%), hypersexuality (24; 35%), compulsive spending/shopping (18; 26%), binge eating (12; 17%), compulsive hobbying (8; 12%) and compulsive computer use (6; 9%).

2) Frequency of new-onset pathologic compulsive gambling or hypersexuality after drug treatment of idiopathic Parkinson disease (2009). Excerpt:

Among the study patients with PD, new-onset compulsive gambling or hypersexuality was documented in 7 (18.4%) of 38 patients taking therapeutic doses of dopamine agonists but was not found among untreated patients, those taking subtherapeutic agonist doses, or those taking carbidopa/levodopa alone.

3) Compulsive eating and weight gain related to dopamine agonist use (2006). Excerpt:

Dopamine agonists have been implicated in causing compulsive behaviors in patients with Parkinson's disease (PD). These have included gambling, hypersexuality, hobbyism, and other repetitive, purposeless behaviors ("punding").

4) Reports of pathological gambling, hypersexuality, and compulsive shopping associated with dopamine receptor agonist drugs (2014). Excerpt:

Severe impulse control disorders involving pathological gambling, hypersexuality, and compulsive shopping have been reported in association with the use of dopamine receptor agonist drugs in case series and retrospective patient surveys. These agents are used to treat Parkinson disease, restless leg syndrome, and hyperprolactinemia. Our findings confirm and extend the evidence that dopamine receptor agonist drugs are associated with these specific impulse


SLIDE 14

For example, give rats unlimited access to enticing junk food and almost all of them will binge to obesity. This is also why 4 out of 5 adult Americans are overweight and half of them obese - that is, addicted to food. In contrast to natural rewards, drugs - such as alcohol or cocaine, will only hook about 10-15% of users, whether humans or rats.

ORIGINAL SUPPORT:

Claim #1: Support for "give rats unlimited access to enticing junk food and almost all of them will binge to obesity" came from this 2010 study: Addiction-like reward dysfunction and compulsive eating in obese rats: Role for dopamine D2 receptors (2010) – Abstract:

We found that development of obesity was coupled with the emergence of a progressively worsening brain reward deficit. Similar changes in reward homeostasis induced by cocaine or heroin is considered a critical trigger in the transition from casual to compulsive drug-taking. Accordingly, we detected compulsive-like feeding behavior in obese but not lean rats, measured as palatable food consumption that was resistant to disruption by an aversive conditioned stimulus. Striatal dopamine D2 receptors (D2R) were downregulated in obese rats, similar to previous reports in human drug addicts. Moreover, lentivirus-mediated knockdown of striatal D2R rapidly accelerated the development of addiction-like reward deficits and the onset of compulsive-like food seeking in rats with extended access to palatable high-fat food. These data demonstrate that overconsumption of palatable food triggers addiction-like neuroadaptive responses in brain reward circuitries and drives the development of compulsive eating. Common hedonic mechanisms may therefore underlie obesity and drug addiction.

A lay article about the above study (2010) – Excerpts:

Brains of rats that gorged themselves on human fatty foods changed.

Dopamine appears to be responsible for the behavior of the overeating rats.

Scientists have finally confirmed what the rest of us have suspected for years: Bacon, cheesecake, and other delicious yet fattening foods may be addictive.

A new study in rats suggests that high-fat, high-calorie foods affect the brain in much the same way as cocaine and heroin. When rats consume these foods in great enough quantities, it leads to compulsive eating habits that resemble drug addiction, the study found.

Doing drugs such as cocaine and eating too much junk food both gradually overload the so-called pleasure centers in the brain, according to Paul J. Kenny, Ph.D., an associate professor of molecular therapeutics at the Scripps Research Institute, in Jupiter, Florida. Eventually the pleasure centers "crash," and achieving the same pleasure--or even just feeling normal--requires increasing amounts of the drug or food, says Kenny, the lead author of the study.

In previous studies, rats have exhibited similar brain changes when given unlimited access to cocaine or heroin. And rats have similarly ignored punishment to continue consuming cocaine, the researchers note.

The fact that junk food could provoke this response isn't entirely surprising, says Dr.Gene-Jack Wang, M.D., the chair of the medical department at the U.S. Department of Energy's Brookhaven National Laboratory, in Upton, New York.

"We make our food very similar to cocaine now," he says.

The neurotransmitter dopamine appears to be responsible for the behavior of the overeating rats, according to the study. Dopamine is involved in the brain's pleasure (or reward) centers, and it also plays a role in reinforcing behavior. "It tells the brain something has happened and you should learn from what just happened," says Kenny.

Overeating caused the levels of a certain dopamine receptor in the brains of the obese rats to drop, the study found. In humans, low levels of the same receptors have been associated with drug addiction and obesity, and may be genetic, Kenny says.

Claim #2: This page contains support for: "4 out of 5 adult Americans are overweight and half of them obese."

Claim #3: This PDF and this study contains support for: "In contrast to natural rewards, drugs - such as alcohol or cocaine, will only hook about 10-15% of users, whether humans or rats." 

Claim #4: In 2011, there was very strong neurobiological support (animal & human studies) for the existence of "food addiction." Neurobiological support continues to accumulate at remarkable rate (see next section and this list of over 300 neurological studies). A few selected reviews published prior to the 2012 TEDx talk:

1) Natural rewards, neuroplasticity, and non-drug addiction (2011) – Abstract:

There is a high degree of overlap between brain regions involved in processing natural rewards and drugs of abuse. “Non-drug” or “behavioral” addictions have become increasingly documented in the clinic, and pathologies include compulsive activities such as shopping, eating, exercising, sexual behavior, and gambling. Like drug addiction, non-drug addictions manifest in symptoms including craving, impaired control over the behavior, tolerance, withdrawal, and high rates of relapse. These alterations in behavior suggest that plasticity may be occurring in brain regions associated with drug addiction. In this review, I summarize data demonstrating that exposure to non-drug rewards can alter neural plasticity in regions of the brain that are affected by drugs of abuse. Research suggests that there are several similarities between neuroplasticity induced by natural and drug rewards and that, depending on the reward, repeated exposure to natural rewards might induce neuroplasticity that either promotes or counteracts addictive behavior.

2) Common cellular and molecular mechanisms in obesity and drug addiction (2011) – Abstract:

The hedonic properties of food can stimulate feeding behaviour even when energy requirements have been met, contributing to weight gain and obesity. Similarly, the hedonic effects of drugs of abuse can motivate their excessive intake, culminating in addiction. Common brain substrates regulate the hedonic properties of palatable food and addictive drugs, and recent reports suggest that excessive consumption of food or drugs of abuse induces similar neuroadaptive responses in brain reward circuitries. Here, we review evidence suggesting that obesity and drug addiction may share common molecular, cellular and systems-level mechanisms.

3) Can Food Be Addictive? Public Health And Policy Implications (2011) – Excerpts:

Data suggest that hyperpalatable foods may be capable of triggering an addictive process. Although the addictive potential of foods continues to be debated, important lessons learned in reducing the health and economic consequences of drug addiction may be especially useful in combating food-related problems.

Although there exist important differences between foods and addictive drugs, ignoring analogous neural and behavioral effects of foods and drugs of abuse may result in increased food-related disease and associated social and economic burdens. Public health interventions that have been effective in reducing the impact of addictive drugs may have a role in targeting obesity and related diseases.

4) Neural Correlates of Food Addiction (2011) – Excerpts:

Research has implicated an addictive process in the development and maintenance of obesity. Although parallels in neural functioning between obesity and substance dependence have been found, to our knowledge, no studies have examined the neural correlates of addictive-like eating behavior.

Similar patterns of neural activation are implicated in addictive-like eating behavior and substance dependence: elevated activation in reward circuitry in response to food cues and reduced activation of inhibitory regions in response to food intake.

5) Food And Addiction: Sugars Fats And Hedonic Overeating. (2011) – Excerpts:

Clearly, not all foods would be candidates for addiction: Gearhardt et al. argue that ‘hyperpalatable’ foods rich in fats, sugars and/or salts, which are often comprised of synthetic combinations of many ingredients, may have greater addictive potential than traditional foods such as fruits, vegetables and lean protein. We know from studies of feeding behavior that different nutrients can affect specific brain neuropeptide and neurotransmitter systems [14,15]. Further, preclinical studies suggest that overeating sugar produces different addiction-like behaviors compared with overeating fat [5].

6) Overeating, Obesity, and Dopamine Receptors (2010) – Excerpts:

The neurotransmitter dopamine plays a key role in the brain reward circuit. The intake of highly addictive drugs such as cocaine causes an increase in dopamine levels in the limbic brain including the nucleus accumbens of the striatum, which leads to reinforcement of associated behaviors (1). Recent studies have also shed light on the involvement of the striatum in feeding in obese humans. Notably, positron emission tomography studies have shown that striatal dopamine D2 receptors are reduced in obese individuals compared with D2 receptors from their leaner counterparts (2). In addition, it has also been demonstrated that obese individuals tend to overeat to compensate for blunted striatal sensitivity (3). Analogous deficiencies in striatal dopamine signaling have also been observed in individuals addicted to drugs. Because pathological overeating is also driven by pleasure and the compulsion to continue despite known negative effects, like drug addiction, it is thought to involve dopamine neurotransmission. However, whether these deficiencies in D2 receptor signaling drive obesity or whether obese individuals develop deficiencies as a result of reward dysfunction is an open question.

7) Obesogenic diets may differentially alter dopamine control of sucrose and fructose intake in rats (2011) – Excerpts:

Chronic overeating of obesogenic diets can lead to obesity, reduced dopamine signaling, and increased consumption of added sugars to compensate for blunted reward. Thus, it appears that obesity due to the consumption of combinations of dietary fat and sugar rather than extra calories from dietary fat alone may result in reduced D2 receptor signaling. Furthermore, such deficits seem to preferentially affect the control of fructose intake.

These findings demonstrate for the first time a plausible interaction between diet composition and dopamine control of carbohydrate intake in diet-induced obese rats. It also provides additional evidence that sucrose and fructose intake is regulated differentially by the dopamine system.

9) Reward Mechanisms in Obesity: New Insights and Future Directions (2011) – Excerpt:

Food is consumed in order to maintain energy balance at homeostatic levels. In addition, palatable food is also consumed for its hedonic properties independent of energy status. Such reward-related consumption can result in caloric intake exceeding requirements and is considered a major culprit in the rapidly increasing rates of obesity in developed countries. Compared with homeostatic mechanisms of feeding, much less is known about how hedonic systems in brain influence food intake. Intriguingly, excessive consumption of palatable food can trigger neuroadaptive responses in brain reward circuitries similar to drugs of abuse. Furthermore, similar genetic vulnerabilities in brain reward systems can increase predisposition to drug addiction and obesity. Here, recent advances in our understanding of the brain circuitries that regulate hedonic aspects of feeding behavior will be reviewed. Also, emerging evidence suggesting that obesity and drug addiction may share common hedonic mechanisms will also be considered.

10) The dark side of food addiction (2011) - Excerpt:

In drug addiction, the transition from casual drug use to dependence has been linked to a shift away from positive reinforcement and towards negative reinforcement. That is, drugs ultimately are relied on to prevent or relieve negative states that otherwise result from abstinence (e.g., withdrawal) or from adverse environmental circumstances (e.g., stress). Recent work has suggested that this “dark side” shift also is key in the development of food addiction. Initially, palatable food consumption has both positive reinforcing, pleasurable effects and negative reinforcing, “comforting” effects that can acutely normalize organism responses to stress. Repeated, intermittent intake of palatable food may instead amplify brain stress circuitry and downregulate brain reward pathways such that continued intake becomes obligatory to prevent negative emotional states via negative reinforcement. Stress, anxiety and depressed mood have shown high comorbidity with and the potential to trigger bouts of addiction-like eating behavior in humans. Animal models indicate that repeated, intermittent access to palatable foods can lead to emotional and somatic signs of withdrawal when the food is no longer available, tolerance and dampening of brain reward circuitry, compulsive seeking of palatable food despite potentially aversive consequences, and relapse to palatable food-seeking in response to anxiogenic-like stimuli. The neurocircuitry identified to date in the “dark” side of food addiction qualitatively resembles that associated with drug and alcohol dependence. The present review summarizes Bart Hoebel’s groundbreaking conceptual and empirical contributions to understanding the role of the “dark side” in food addiction along with related work of those that have followed him

UPDATED SUPPORT:

Hundreds of animal and human studies supporting claim #4 (existence of food addiction) have been published since 2011. For example "food addiction" returns 7,400 citations from Google scholar, while "food addiction" + neurobiology returns 3,330 citations from Google scholar. From this list of over 300 neurological studies, I've selected a few recent reviews to further support the food-addiction model:

  1. Obesity And Addiction: Neurobiological Overlaps (2012) Nora Volkow
  2. Obesity is associated with altered brain function: sensitization and hypofrontality (2012)
  3. The obesity epidemic and food addiction: clinical similarities to drug dependence (2012)
  4. The obesity epidemic: the role of addiction (2012)
  5. Striatocortical Pathway Dysfunction in Addiction And Obesity: Differences and Similarities (2013) Nora Volkow
  6. The overlap between binge eating disorder and substance use disorders: Diagnosis and neurobiology (2013)
  7. A common biological basis of obesity and nicotine addiction (2013)
  8. The Addictive Dimensionality of Obesity (2013)
  9. Animal Models of Compulsive Eating Behavior (2014)
  10. Are Certain Foods Addictive? - A reply (2014)
  11. Food Addiction in the Light of DSM-5 (2014)
  12. Binge eating in pre-clinical models (2015)
  13. Current considerations regarding food addiction (2015)
  14. Which Foods May Be Addictive? The Roles of Processing, Fat Content, and Glycemic Load (2015)
  15. Neurobiological features of binge eating disorder (2015)
  16. Aberrant mesolimbic dopamine-opiate interaction in obesity (2015)
  17. Food addiction as a new piece of the obesity framework (2015)
  18. Addiction-like Synaptic Impairments in Diet-Induced Obesity (2016)
  19. Allostasis in health and food addiction: fMRI (2016)
  20. Behavioral sensitization of the reinforcing value of food: What food and drugs have in common (2016)
  21. Food Addiction as a new behavioral addiction (2016)
  22. Psychological and Neurobiological Correlates of Food Addiction (2016)
  23. The Influence of Palatable Diets in Reward System Activation: A Mini Review (2016)
  24. Largely overlapping neuronal substrates of reactivity to drug, gambling, food and sexual cues: A comprehensive meta-analysis (2016)
  25. The Neurobiology of "Food Addiction" and Its Implications for Obesity Treatment and Policy (2016)
  26. Food and drug addictions: Similarities and differences (2017)
  27. Food for Thought: Reward Mechanisms and Hedonic Overeating in Obesity (2017)
  28. Overlapping Neural Endophenotypes in Addiction and Obesity (2017)
  29. Palatable Hyper-Caloric Foods Impact on Neuronal Plasticity (2017)
  30. Pathological Overeating: Emerging Evidence for a Compulsivity Construct (2017)

Interestingly, a 2017 review of the literature proposed a model of compulsive internet porn use that parallels the very simple model presented in Slides 13-17 (Pornography, Pleasure, and Sexuality: Towards a Hedonic Reinforcement Model of Sexually Explicit Internet Media Use). It proposes that both highly palatable foods and streaming internet porn contain unique properties that may be perceived as especially rewarding to the consumer. Put simply both junk food and streaming internet porn can override satiation mechanisms and supplant traditional versions of sex and food. A few excerpts from the review:

Theoretical rationale

Whereas prior works have conceptualized IPU as analogous to gambling (e.g., King, 1999) or even substance use (e.g., Park et al., 2016), the theoretical rationale for the present model is strongly supported by recent work on another physiological drive: hunger. Theories and models of hunger and food consumption serve as a logical comparison that could inform the conceptualization of sexual motives and behaviors, given that both have similarities in evolutionary development, that both sexual activity and food consumption are required for survival, that both provide hedonic rewards, that both are centrally motivating to many human behaviors, and that both seem to be only be temporarily satiated when indulged. Working from this analogue, a body of recent literature has popularized the notions of hedonic hunger (Lowe & Butryn, 2007). Rather than being motivated by caloric need, hedonic hunger refers specifically to the desire for food due to the pleasure that it brings the consumer (Lowe & Butryn, 2007). Although hedonic motives have likely always been a part of the hunger drive, this distinction between hedonic hunger and physiological hunger has increased with recent advances in the production of hyperpalatable foods, or foods that are designed to powerfully appeal to specific evolutionarily derived flavor preferences (e.g., salty, fatty, sweet; Avena & Gold, 2011; Gearhardt, Davis et al., 2011; Gearhardt, Davis, Kuschner, & Brownell, 2011). These foods are relatively recent (in the context of human evolution) developments that both reward individuals powerfully and promote behavior change.

On an individual level, hyperpalatable foods can promote change in behaviors, but they are also likely responsible for cultural dietary changes in developed countries (Fortuna, 2012). As food has become more palatable, eating has also become more rewarding, and consequently, pleasure-seeking motivations for food consumption have risen. Collectively, these factors have changed the way in which many people approach hunger and food on both individual and cultural levels (for a review, see Pinel et al., 2000), with Western societies—particularly the U.S.—becoming more hedonic in their approach to food.

Throughout the present work, we posit that IP represents a similar cultural phenomenon to hyperpalatable food and hedonic hunger in regards to sexual motivation and sex-related goals. Each component of our proposed model parallels findings in the eating literature, and the comparisons will be discussed in more detail below. In sum, prior literature indicates that hedonic hunger is reinforced via indulgence in uniquely reinforcing hyperpalatable foods, thereby leading to more hedonic approaches to food and eating. In like fashion, we argue that IP is consumed primarily for hedonic reasons; that it is uniquely reinforcing due to its accessibility, customizability, novelty, and variety; and that it is likely promoting more hedonic approaches to sexuality

Sexual Addiction

As was reviewed at the outset of this work, much of the previous literature on IPU has focused on themes of addiction, compulsivity, and impulsivity (Short et al., 2012). More to the point, there is a clear contention in early academic (e.g., Cooper et al., 1998) and current popular (e.g., Foubert, 2016; Wilson, 2014) literature that IP has addictive qualities. Indeed, the research literature is replete with case studies and clinical examples of individuals who have sought treatment for IP addiction (e.g., Ford, Durtschi, & Franklin, 2012; Gola & Potenza, 2016; Griffiths, 2000; Kraus, Meshberg-Cohen, Martino, & Potenza, 2015), often describing individuals experiencing profound disruption and negative consequences associated with IPU. Furthermore, the notion of problematic or excessive IPU is not controversial, with several empirical studies documenting how some individuals may become compulsive or excessive in their use (e.g., Crosby & Twohig, 2016; For et al., 2014; Sirianni & Vishwanath, 2016). Despite this, numerous peer-reviewed syntheses have concluded that referring to typical IPU as addictive is a premature judgement (e.g., Duffy et al., 2016; Kraus, Voon, & Potenza, 2016; Reid, 2016).

Rather than engaging with the nuances of such a debate, the present model organizes the literature in a way that might more accurately account for addiction or compulsivity than previous models have. This conjecture is supported by recent work with our model’s theoretical parallel: hunger. A highly rewarding stimulus that satiates a biological drive clearly has the potential for excessive use or abuse (e.g., Gearhardt, Yokum, et al., 2011). Within appetite and obesity literature, the notion of food addiction has recently garnered much attention (e.g., Gearhardt, White, Masheb, & Grilo, 2013; Hebebrand et al., 2014; Smith & Robbins, 2013). Although this model for understanding compulsive food consumption is not without controversy (e.g., Benton & Young, 2016; Ziauddeen & Fletcher, 2013), it has proven to be a useful concept for the understanding and classification of problematic, compulsive, or excessive eating behaviors (Avena, Gearhardt, Gold, Wang, & Potenza, 2012). Using this literature as an exemplar then, it is likely that addiction and compulsivity models of problematic of IPU also have some utility in accounting for excessive or disruptive IPU.

It is likely that the debate over the correct classification of problematic IPU as an addiction, a compulsion, or an impulse control disorder will continue for many years (e.g., Reid, 2016). However, the present model seeks to frame IPU in a way that does not rely on notions of IP as inherently addictive. As a highly-rewarding stimulus, IPU will likely influence different individuals in unique ways. In much the same way that some individuals may be more prone to food addiction or other behavioral dysregulations such as pathological gambling, certain people may be more sensitive to the highly rewarding nature of IP, which may result in problematic behavior patterns developing.


SLIDE 15

This "binge mechanism" for food and sex was once an evolutionary advantage. It helped us “get it while the getting was good”. Think of wolves stowing away 20 pounds of meat per kill. Or it’s mating season and you’re the alpha male.

ORIGINAL & UPDATED SUPPORT:

The claim: That "binge mechanism" for food and sex exists.

Binge mechanisms involve chronically elevated dopamine inducing sensitization, and perhaps desensitization (expanded upon in Slide 18, Slide 13, Slide 14, and Slide 16). Here I present a synopsis of how sensitization and desensitization promote bingeing. In addition, other recently identified "binge mechanisms" for highly palatable foods are provided.

Sensitization leads to increased wanting, cravings, and inability to control use. This is sufficient to induce bingeing (as it does with fully developed addictions). Desensitization can amplify the cravings induced by sensitization.

Sensitization: As described in other slides, continued over-consumption of natural rewards (sex, sugar, high-fat, aerobic exercise) or chronic administration of virtually any drug of abuse causes DeltaFosB to slowly accumulate in much of the reward system (PFC, nucleus accumbens). DeltaFosB activates certain genes which initiate several brain changes, primarily sensitization. This manifests as cue-reactivity, severe cravings, and difficulty controlling use. Cue reactivity and strong cravings to use are markers for addiction, and can be assessed via brain imaging and neuropsychological assessments or self-reports. As of 2017, twenty studies reporting sensitization or cue-reactivity/cravings in porn users or sex addicts have been published: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20.

Desensitization: As increased cravings compel the user to binge on porn, overstimulation of the reward circuitry leads to a localized rebellion. If DeltaFosB is the gas pedal for bingeing, the molecule CREB functions as the brakes. CREB dampens our pleasure response. It inhibits dopamine. CREB is trying to take the joy out of bingeing so that you give it a rest.

Oddly enough, high levels of dopamine stimulate the production of both CREB and DeltaFosB. But the glitch in the CREB/DeltaFosB balancing act is that it evolved long before humans were exposed to powerful reinforcers such as whiskey, cocaine, ice cream, or porn tube sites. All have the potential to override evolved satiation mechanisms, including CREB’s brakes. Continued overconsumption may also lead to a fairly rapid decline in dopamine D2 receptors (as occurred with rats binging on junk food). This can intensify cravings as D2 receptors function to inhibit over-consumption of drugs and natural rewards. Desensitization leads to tolerance, which is the need for a higher does to achieve the same effect. As of 2017 six studies on porn users report findings consistent with desensitization or habituation: 1, 2, 3, 4, 5, 6.

You may be wondering how chronic overstimulation can induce two seemingly opposite effects. First, it can increase dopamine activity (sensitization via DeltaFosB). Second, it can decrease dopamine activity (desensitization via CREB). The answer is that it’s mostly about timing. But it’s also about the neurological differences between wanting and liking.

Sensitization leads to high spikes of dopamine in response to cues and triggers associated with use. The dopamine spikes occur before ingesting the drug or masturbating to porn, and are experienced as cravings to use. However, on exposure to the same old stimuli less dopamine (and less opioids) are released (desensitization). This dampening of pleasure occurs during drug use or while masturbating to porn. The activity is experienced as less pleasurable, increasing cravings for more.

The following studies describe diverse mechanisms by which highly palatable food induces sensitization and resultant bingeing:

1) Study Finds Why We Crave Chips & Fries (2011) - Excerpts:

Fatty foods like chips and fries trigger the body to produce chemicals much like those found in marijuana, researchers report today in the journal Proceedings of the National Academy of Sciences (PNAS). These chemicals, called "endocannabinoids," are part of a cycle that keeps you coming back for just one more bite of cheese fries, the study found.

The results showed that fat on the tongue triggers a signal to the brain, which then relays a message down to the gut via a nerve bundle called the vagus nerve. This message commands the production of endocannabinoids in the gut, which in turn drives a cascade of other signals all pushing the same message: Eat, eat, eat!

This message would have been helpful in the evolutionary history of mammals, Piomelli said. Fats are crucial to survival, and they were once hard to come by in the mammalian diet. But in today's world, where a convenience store full of junk food sits on every corner, our evolutionary love of fat easily backfires.

2) Insulin action in the brain can lead to obesity (2011) – High fat diet induces neurochemical cascade that promotes consumption and reduces energy expenditure. Excerpts:

Fat-rich food makes you fat. Behind this simple equation lie complex signalling pathways, through which the neurotransmitters in the brain control the body's energy balance.

The consumption of high-fat food causes more insulin to be released by the pancreas. This triggers a signalling cascade in special nerve cells in the brain, the SF-1 neurons, in which the enzyme P13-kinase plays an important role. Over the course of several intermediary steps, the insulin inhibits the transmission of nerve impulses in such a way that the feeling of satiety is suppressed and energy expenditure reduced. This promotes overweight and obesity.

The hypothalamus plays an important role in energy homeostasis: the regulation of the body's energy balance. Special neurons in this part of the brain, known as POMC cells, react to neurotransmitters and thus control eating behaviour and energy expenditure. When high-fat food is consumed, more insulin is produced in the pancreas, and its concentration in the brain also increases. The interaction between the insulin and the target cells in the brain also plays a crucial role in the control of the body's energy balance.

"Therefore, in overweight people, insulin probably indirectly inhibits the POMC neurons, which are responsible for the feeling of satiety, via the intermediary station of the SF-1 neurons," supposes the scientist. "At the same time, there is a further increase in food consumption." The direct proof that the two types of neurons communicate with each other in this way still remains to be found, however.

With normal food consumption, the researchers discovered no difference between the two groups. This would indicate that insulin does not exercise a key influence on the activity of these cells in slim individuals. However, when the rodents were fed high-fat food, those with the defective insulin receptor remained slim, while their counterparts with functional receptors rapidly gained weight. The weight gain was due to both an increase in appetite and reduced calorie expenditure. This effect of insulin could constitute an evolutionary adaptation by the body to an irregular food supply and extended periods of hunger: if an excess supply of high-fat food is temporarily available, the body can lay down energy reserves particularly effectively through the action of insulin.

3) Intestinal lipid–derived signals that sense dietary fat (2014) - Here researchers found that short-term ingestion of concentrated fats induces chemical signals promoting satiation, while prolonged consumption of dietary fat reduces satiation mechanisms. Excerpt:

In summary, the available data indicate that OEA, generated by small-intestinal enterocytes during the digestion of fat-containing foods, causes satiety through a paracrine PPARα-mediated mechanism that requires the recruitment of afferent sensory fibers. This response also depends on the presence of an intact sympathetic nervous system — which may function to facilitate fat-induced OEA production in the gut — and engages oxytocin, histamine, and dopamine transmission in the CNS. The intriguing but as yet unexplained observation that prolonged exposure to dietary fat lowers small intestinal OEA levels (124, 125) raises questions about the mechanism regulating OEA signaling in the gut and the possible role it might play in overeating and obesity.

4) How junk food primes the brain's food-seeking behavior (2015) - Consumption of extremely palatable food—specifically, sweetened high-fat food— induces neuroplastic changes of dopamine producing neurons. In essence, sensitization. This led to greater seeking. Excerpts:

(Medical Xpress)—The current epidemic of obesity in developed countries should be a warning for health officials in the developing world with newly opened markets. Food manufacturers, restaurant franchising companies, food supply chains and advertisers collaborate to create environments in which extremely palatable, energy-dense foods and their related cues are readily available; however, people still have adaptive neural architecture best suited for an environment of food scarcity. In other words, the brain's programming may make it difficult to handle the modern food ecosystem in a metabolically healthy way.

Humans, like all animals, have ancient genetic programming adapted specifically to ensure food intake and food-seeking survival behaviors. Environmental cues strongly influence these behaviors by altering neural architecture, and corporations have refined the science of leveraging human pleasure response and perhaps inadvertently reprogramming people's brains to seek surplus calories. In an environment that is rich in highly palatable, energy-dense foods, the pervasiveness of food-related cues can lead to food seeking and overeating regardless of satiety, a likely driver of obesity.

A group of Canadian researchers at the University of Calgary and the University of British Columbia recently published the results of a mouse study in the Proceedings of the National Academy of Sciences in which they explored the neural mechanisms behind these changes in food-seeking behavior.

They report that the short-term consumption of extremely palatable food—specifically, sweetened high-fat food—actually primes future food approach behaviors. They found that the effect is mediated by the strengthening of excitatory synaptic transmission onto dopamine neurons, and lasts for days after initial 24-hour exposure to sweetened high-fat foods.

These changes occur in the brain's ventral tegmental area (VTA) and its mesolimbic projections, an area involved in adapting to environmental cues used for predicting motivationally relevant outcomes—in other words, the VTA is responsible for creating cravings for stimuli found to be rewarding in some way.

The researchers write, "Because enhanced excitatory synaptic transmission onto dopamine neurons is thought to transform neutral stimuli to salient information, these changes in excitatory synaptic transmission may underlie the increased food-approach behavior observed days after exposure to sweetened high-fat foods and potentially prime increased food consumption."

The enhanced synaptic strength lasts for days after exposure to high-energy-density food, and is mediated by increased excitatory synaptic density. The researchers found that introducing insulin directly to the VTA suppresses excitatory synaptic transmission onto dopamine neurons and completely suppresses food-seeking behaviors observed after 24-hour access to sweetened high-fat food.

More information: Consumption of palatable food primes food approach behavior by rapidly increasing synaptic density in the VTA. PNAS 2016 ; published ahead of print February 16, 2016, DOI: 10.1073/pnas.1515724113

5) Do Orexins contribute to impulsivity-driven binge consumption of rewarding stimulus and transition to drug/food dependence? (2015) – Bingeing on addictive drugs and junk food involve the same mechanisms (meaning that drugs hijack the evolutionary mechanisms in place for bingeing on food).

Orexins (OX) are neuropeptides synthesized in the lateral hypothalamic region which play a fundamental role in a wide range of physiological and psychological functions including arousal, stress, motivation or eating behaviors. This paper reviews under the addiction cycle framework (Koob, 2010), the role of the OX system as a key modulator in compulsivity-driven consumption of rewarding stimulus including ethanol, palatable food and drugs and their role in impulsivity and binge-like consumption in non dependent organisms as well.

We propose here that drug/food binge-like consumption in vulnerable organisms increases OX activity which, in turn, elicits enhanced impulsivity and further impulsivity-driven binge consumption in a positive loop that would promote compulsive-driven binge-consumption and the transition to drug/food disorders over time.

6) Escalation in high fat intake in a binge eating model differentially engages dopamine neurons of the ventral tegmental area and requires ghrelin signaling (2015) - High fat diet induces bingeing via dopamine-based mechanisms. Excerpts:

Binge eating is a behavior observed in a variety of human eating disorders. Ad libitum fed rodents daily and time-limited exposed to a high-fat diet (HFD) display robust binge eating events that gradually escalate over the initial accesses. Intake escalation is proposed to be part of the transition from a controlled to a compulsive or loss of control behavior. Here, we used a combination of behavioral and neuroanatomical studies in mice daily and time-limited exposed to HFD to determine the neuronal brain targets that are activated - as indicated by the marker of cellular activation c-Fos - under these circumstances. Also, we used pharmacologically or genetically manipulated mice to study the role of orexin or ghrelin signaling, respectively, in the modulation of this behavior.

We found that four daily and time-limited accesses to HFD induce: (i) a robust hyperphagia with an escalating profile, (ii) an activation of different sub-populations of the ventral tegmental area dopamine neurons and accumbens neurons that is, in general, more pronounced than the activation observed after a single HFD consumption event, and (iii) an activation of the hypothalamic orexin neurons, although orexin signaling blockage fails to affect escalation of HFD intake. In addition, we found that ghrelin receptor-deficient mice fail to both escalate the HFD consumption over the successive days of exposure and fully induce activation of the mesolimbic pathway in response to HFD consumption. Current data suggest that the escalation in high fat intake during repeated accesses differentially engages dopamine neurons of the ventral tegmental area and requires ghrelin signaling.

7) Opioid system in the medial prefrontal cortex mediates binge-like eating (2013) – Highly palatable food activated an opioid based binge mechanism in rats. Excerpts:

Binge eating disorder is an addiction-like disorder characterized by excessive food consumption within discrete periods of time.

This study was aimed at understanding the role of the opioid system within the medial prefrontal cortex (mPFC) in the consummatory and motivational aspects of binge-like eating. For this purpose, we trained male rats to obtain either a sugary, highly palatable diet (Palatable rats) or a chow diet (Chow rats) for 1 hour/day.

We then evaluated the effects of the opioid receptor antagonist, naltrexone, given either systemically or site-specifically into the nucleus accumbens (NAcc) or the mPFC on a fixed ratio 1 (FR1) and a progressive ratio schedule of reinforcement for food.

Finally, we assessed the expression of the genes proopiomelanocortin (POMC), pro-dynorphin (PDyn) and pro-enkephalin (PEnk), coding for the opioids peptides in the NAcc and the mPFC in both groups.

Palatable rats rapidly escalated their intake by four times. Naltrexone, when administered systemically and into the NAcc, reduced FR1 responding for food and motivation to eat under a progressive ratio in both Chow and Palatable rats; conversely, when administered into the mPFC, the effects were highly selective for binge eating rats. Furthermore, we found a twofold increase in POMC and a ∼50% reduction in PDyn gene expression in the mPFC of Palatable rats, when compared to control rats; however, no changes were observed in the NAcc.

Our data suggest that neuroadaptations of the opioid system in the mPFC occur following intermittent access to highly palatable food, which may be responsible for the development of binge-like eating.


SLIDE 16
 

 What if mating season never ends? All those hits of dopamine do 2 things:

  • First, they tell your brain that you’ve hit the evolutionary jackpot.
  • Second, (very important) they trigger a molecular switch called…

ORIGINAL SUPPORT:

Slide 16 has no specific claims. It's a transition between slides 14/15 and slide 17.


SLIDE 17

DeltaFosB – which starts to accumulate in your brain's reward circuit. With excess chronic consumption of drugs or natural rewards, this build-up of DeltaFosB (starts to change brain and) promotes a cycle of bingeing and craving.

ORIGINAL SUPPORT:

The slide's claim: Chronically elevated dopamine, in response to a rewarding stimulus, can cause the build-up DeltaFosB, which induces wanting (sensitization).

This slide's claim is supported in the scientific literature. Excess chronic consumption of addictive drugs or natural rewards (including sexual rewards) can lead to the accumulation of DeltaFosB, which in turn leads to sensitization and cravings to use. See the following lists of 130 studies:

Specifically, neurological studies have found that all addictions, both chemical and behavioral, appear to share a key molecular switch: DeltaFosB. Studies reveal that both sexual arousal/orgasm and addictive drugs (cocaine, meth) induce the same molecular mechanisms, which generate similar fundamental brain changes within the same reward system neurons. Put simply, chronically elevated phasic dopamine triggers the production of DeltaFosB. This in turn produces sensitization – the core brain change in both addiction and sexual conditioning.

Here are a few of the many studies published prior to 2012 that supported this slide's assertions:

1) DeltaFosB: A sustained molecular switch for addiction (2001) - Excerpt:

Together, these early findings suggest that ΔFosB, in addition to increasing sensitivity to drugs of abuse, produces qualitative changes in behavior that promote drug-seeking behavior. Thus, ΔFosB may function as a sustained “molecular switch” that helps initiate and then maintain crucial aspects of the addicted state.

2) DeltaFosB: A Molecular Gate to Motivational Processes within the Nucleus Accumbens? (2006) - Excerpt:

The nucleus accumbens (NAc) has long been seen as the interface between limbic and motor systems on the basis of its convergent glutamatergic inputs from many limbic cortical structures, such as the prefrontal cortex, and its outputs to structures involved in motor control, such as the pallidum. The NAc also receives a major dopaminergic innervation from the ventral tegmental area via the mesolimbic pathway that is intimately involved in reward-related processes and addiction. Within the NAc, dopaminergic and glutamatergic inputs might interact to control goal-directed instrumental behavior (response–outcome processes) driven by natural rewards (food, water, sex) or drugs of abuse, and conditioned stimuli associated with them.

Repeated drug exposure induces long-lasting cellular and molecular changes within the NAc that are thought to contribute to the protracted compulsive behavior associated with addiction. Among such adaptations, the induction of the transcription factor ΔFosB within the dynorphin-positive medium spiny neurons is of major interest. ΔFosB has been the first long-lasting transcriptional regulator shown to be involved in the plastic processes associated with the transition to addiction.

These results clearly show that overexpression of ΔFosB in the NAc enhances instrumental responding and increases motivation for food. ΔFosB is thus suggested to be a general molecular switch involved in the modulation of motivational aspects of goal-directed behavior.

3) Sexual experience in female rodents: cellular mechanisms and functional consequences (2006) - Excerpt:

The elevation in dopamine release in experienced female hamsters is reminiscent of the effects of repeated exposure of animals to drugs of abuse [75]. In this literature, the heightened level of dopamine in response to a fixed dose of drug is termed “sensitization” [75]. Drug sensitization is accompanied by a variety of cellular responses thought to enhance synaptic efficacy and information flow through the mesolimbic pathway. Repeated administration of a variety of abused substances with different pharmacological profiles will increase dendritic length and/or spine density in the terminal dendritic branches of medium spiny neurons [13,23,44,45,64,76,77,78]...... Far fewer examples exist for behavioral experience producing comparable effects on dendrites, though induction of salt appetite [79], male sexual behavior [24] and female sexual behavior [59] will alter dendritic morphology in medium spiny neurons of the nucleus accumbens.

4) The Influence of ΔFosB in the Nucleus Accumbens on Natural Reward Related Behavior (2008) - Excerpt:

The transcription factor deltaFosB (ΔFosB), induced in nucleus accumbens (NAc) by chronic exposure to drugs of abuse, has been shown to mediate sensitized responses to these drugs. However, less is known about a role for ΔFosB in regulating responses to natural rewards. Here, we demonstrate that two powerful natural reward behaviors, sucrose drinking and sexual behavior, increase levels of ΔFosB in the NAc. We then use viral-mediated gene transfer to study how such ΔFosB induction influences behavioral responses to these natural rewards. We demonstrate that overexpression of ΔFosB in the NAc increases sucrose intake and promotes aspects of sexual behavior This work suggests that ΔFosB is not only induced in the NAc by drugs of abuse, but also by natural rewarding stimuli. Additionally, our findings show that chronic exposure to stimuli that induce ΔFosB in the NAc can increase consumption of other natural rewards.

5) Transcriptional mechanisms of addiction: role of ΔFosB (2008) - Excerpt:

The effects of ΔFosB may extend well beyond the regulation of drug sensitivity per se to more complex behaviours related to the addiction process. Mice overexpressing ΔFosB work harder to self-administer cocaine in progressive ratio self-administration assays, suggesting that ΔFosB may sensitize animals to the incentive motivational properties of cocaine and thereby lead to a propensity for relapse after drug withdrawal (Colby et al. 2003). ΔFosB-overexpressing mice also show enhanced anxiolytic effects of alcohol (Picetti et al. 2001), a phenotype that has been associated with increased alcohol intake in humans. Together, these early findings suggest that ΔFosB, in addition to increasing sensitivity to drugs of abuse, produces qualitative changes in behaviour that promote drug-seeking behaviour, and support the view, stated above, that ΔFosB functions as a sustained molecular switch for the addicted state.

These findings suggest that ΔFosB in this brain region sensitizes animals not only for drug rewards but for natural rewards as well, and may contribute to states of natural addiction.

6) DeltaFosB Overexpression In The Nucleus Accumbens Enhances Sexual Reward In Female Syrian Hamsters (2009) - Excerpt:

Repeated activation of the mesolimbic dopamine system results in persistent behavioral alterations accompanied by a pattern of neural plasticity in the nucleus accumbens (NAc). As the accumulation of the transcription factor ΔFosB may be an important component of this plasticity, the question addressed in our research is whether ΔFosB is regulated by sexual experience in females. We have shown that female Syrian hamsters given sexual experience exhibit several behavioral alterations including increased sexual efficiency with naïve male hamsters, sexual reward, and enhanced responsiveness to psychomotor stimulants (e.g., amphetamine).

We recently demonstrated that sexual experience increased the levels of ΔFosB in the NAc of female Syrian hamsters. The focus of this study was to explore the functional consequences of this induction by determining if the constitutive overexpression of ΔFosB by adeno-associated viral (AAV) vectors in the NAc could mimic the behavioral effects of sexual experience.

Animals with AAV-mediated overexpression of ΔFosB in the NAc showed evidence of sexual reward in a conditioned place preference paradigm under conditions in which control animals receiving an injection of AAV-green fluorescent protein (GFP) into the NAc did not. Sexual behavior tests further showed that males paired with the AAV-ΔFosB females had increased copulatory efficiency as measured by the proportion of mounts that included intromission compared to males mated with the AAV-GFP females. These results support a role for ΔFosB in mediating natural motivated behaviors, in this case female sexual behavior, and provide new insight into the possible endogenous actions of ΔFosB.

7) Neuroplasticity in the Mesolimbic System Induced by Natural Reward and Subsequent Reward Abstinence (2010) - Excerpt:

Sexual experience induces functional and morphological alterations in the mesolimbic system similar to repeated exposure to psychostimulants. Moreover, abstinence from sexual behavior after repeated mating was essential for increased reward for drugs and dendritic arbors of NAc neurons, suggesting that the loss of sexual reward might also contribute to neuroplasticity of the mesolimbic system. These results suggest that some alterations in the mesolimbic system are common for natural and drug reward and might play a role in general reinforcement.

8) DeltaFosB in The Nucleus Accumbens is Critical For Reinforcing Effects of Sexual Reward (2010) - Excerpt:

Sexual experience was shown to cause ΔFosB accumulation in several limbic brain regions including the nucleus accumbens (NAc), medial prefrontal cortex, ventral tegmental area and caudate putamen but not the medial preoptic nucleus. Finally, ΔFosB levels and its activity in the NAc were manipulated using viral-mediated gene transfer to study its potential role in mediating sexual experience and experience-induced facilitation of sexual performance. Animals with ΔFosB overexpression displayed enhanced facilitation of sexual performance with sexual experience relative to controls. Together, these findings support a critical role for ΔFosB expression in the NAc for the reinforcing effects of sexual behavior and sexual experience-induced facilitation of sexual performance.

Again, Professor Norman Doidge's 2007 bestseller, "The Brain That Changes Itself" suggested that internet pornography addiction exists, and likely involves the buildup of DeltaFosB. Excerpts in support of this slide:

The addictiveness of Internet pornography is not a metaphor. Not all addictions are to drugs or alcohol. People can be seriously addicted to gambling, even to running. All addicts show a loss of control of the activity, compulsively seek it out despite negative consequences, develop tolerance so that they need higher and higher levels of stimulation for satisfaction, and experience withdrawal if they can't consummate the addictive act.

All addiction involves long-term, sometimes lifelong, neuroplastic change in the brain. For addicts, moderation is impossible, and they must avoid the substance or activity completely if they are to avoid addictive behaviors. Alcoholics Anonymous insists that there are no "former alcoholics" and makes people who haven't had a drink for decades introduce themselves at a meeting by saying, "My name is John, and I am an alcoholic." In terms of [brain] plasticity, they are often correct.

In order to determine how addictive a street drug is, researchers at the National Institutes of Health (NIH) in Maryland train a rat to press a bar until it gets a shot of the drug. The harder the animal is willing to work to press the bar, the more addictive the drug. Cocaine, almost all other illegal drugs, and even nondrug addictions such as running make the pleasure-giving neurotransmitter dopamine more active in the brain. Dopamine is called the reward transmitter, because when we accomplish something—run a race and win—our brain triggers its release. Though exhausted, we get a surge of energy, exciting pleasure, and confidence and even raise our hands and run a victory lap. The losers, on the other hand, who get no such dopamine surge, immediately run out of energy, collapse at the finish line, and feel awful about themselves. By hijacking our dopamine system, addictive substances give us pleasure without our having to work for it.

Dopamine, as we saw in Merzenick's work, is also involved in plastic change. The same surge of dopamine that thrills us also consolidates the neuronal connections responsible for the behaviors that led us to accomplish our goal. When Merzenick used an electrode to stimulate an animal's dopamine reward system while playing a sound, dopamine release stimulated plastic change, enlarging the representation for the sound in the animal's auditory map. An important link with porn is that dopamine is also released in sexual excitement, increasing the sex drive in both sexes, facilitating orgasm, and activating the brain's pleasure centers. Hence the addictive power of pornography.

Eric Nestler, at the University of Texas, has shown how addictions cause permanent changes in the brains of animals. A single dose of many addictive drugs will produce a protein, called delta FosB that accumulates in the neurons. Each time the drug is used, more delta FosB accumulates until it throws a genetic switch, affecting which genes are turned on or off. Flipping this switch causes changes that persist long after the drug is stopped, leading to irreversible damage to the brain’s dopamine system and rendering the animal far more prone to addiction. Non-drug addictions, such as running and sucrose drinking, also lead to the accumulation of deltaFosB and the same permanent changes in the dopamine system.

Pornographers promise healthy pleasure and relief from sexual tension, but what they often deliver is addiction, tolerance, and an eventual decrease in pleasure. Paradoxically, the male patients I worked with often craved pornography but didn’t like it. The usual view is that an addict goes back for more of his fix because he likes the pleasure it gives and doesn't like the pain of withdrawal. But addicts take drugs when there is no prospect of pleasure, when they know they have an insufficient dose to make them high, and will crave more before they begin to withdraw. Wanting and liking are two different things.

An addict experiences cravings because his plastic brain has become sensitized to the drug or the experience. Sensitization leads to increased wanting. It is the accumulation of deltaFosB, caused by exposure to an addictive substance or activity, that leads to sensitization.

Pornography is more exciting than satisfying because we have two separate pleasure systems in our brains, one that has to do with exciting pleasure and one with satisfying pleasure. The exciting system relates to the "appetitive" pleasure that we get imagining something we desire, such as sex or a good meal. Its neurochemistry is largely dopamine-related, and it raises our tension level.

The second pleasure system has to do with the satisfaction, or consummatory pleasure, that attends actually having sex or having that meal, a calming, fulfilling pleasure. Its neurochemistry is based on the release of endorphins, which are related to opiates and give a peaceful, euphoric bliss.

Pornography, by offering an endless harem of sexual objects, hyperactivates the appetitive system. Porn viewers develop new maps in their brains, based on the photos and videos they see. Because it is a use-it-or-lose-it brain, when we develop a map area, we long to keep it activated. Just as our muscles become impatient for exercise if we've been sitting all day, so too do our senses hunger to be stimulated.

The men at their computers looking at porn were uncannily like the rats in the cages of the NIH, pressing the bar to get a shot of dopamine or its equivalent. Though they didn't know it, they had been seduced into pornographic training sessions that met all the conditions required for plastic change of brain maps. Since neurons that fire together wire together, these men got massive amounts of practice wiring these images into the pleasure centers of the brain, with the rapt attention necessary for plastic change. They imagined these images when away from their computers, or while having sex with their girlfriends, reinforcing them. Each time they felt sexual excitement and had an orgasm when they masturbated, a "spritz of dopamine," the reward neurotransmitter, consolidated the connections made in the brain during the sessions. Not only did the reward facilitate the behavior; it provoked none of the embarrassment they felt purchasing Playboy at a store. Here was a behavior with no “punishment,” only reward.

The content of what they found exciting changed as the Web sites introduced themes and scripts that altered their brains without their awareness. Because plasticity is competitive, the brain maps for new, exciting images increased at the expense of what had previously attracted them—the reason, I believe, they began to find their girlfriends less of a turn-on.

UPDATED SUPPORT:

It's important to note that DeltaFosB rapidly degrades, which means it must be assessed in active addicts. Moreover, DeltaFosB levels can only be ascertained post mortem. Due to this limitation, human reward system levels of DeltaFosB have only been measured in one study on cocaine addicts who committed suicide or died without prolonged illnesses: Behavioral and Structural Responses to Chronic Cocaine Require a Feed-forward Loop Involving ΔFosB and Calcium/Calmodulin-Dependent Protein Kinase II in the Nucleus Accumbens Shell (2013). As expected, the cocaine addicts' reward systems contained abnormally high levels of DeltaFosB.

As described, chronically elevated dopamine triggers DeltaFosB, which in turns produces sensitization – the core brain change in both addiction and sexual conditioning. Sensitization leads to cue-reactivity, severe cravings, and difficulty controlling use once use is initiated. Cue-reactivity and strong "cravings to use" are markers for addiction, and can be assessed via brain imaging and neuropsychological assessments or self reports. Since December 2011, twenty studies reporting sensitization or cue-reactivity in porn users or sex addicts have been published: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20. This alone fully supports the claims made in Slide 17.

A neurological paper published after my TEDx talk discusses the significance of DeltaFosB in compulsive sexual behaviors: Pornography addiction – a supranormal stimulus considered in the context of neuroplasticity (2013). An excerpt:

To accept the evidence supporting the concept of sexual addiction, it is necessary to have an understanding of the current concepts of cellular learning and plasticity. Dendritic arborization and other cellular changes precede gyral sculpting (Zatorre, Field, & Johansen-Berg, 2012 Zatorre R. J, Field R. D, Johansen-Berg H. Plasticity in gray and white: Neuroimaging changes in brain structure during learning. Nature Neuroscience. 2012; 15: 528–536. [Google Scholar]) with learning, and reward-based learning is no different. Addiction thus becomes a powerful form of learning, with the associated neuroplasticity being detrimental (Kauer & Malenka, 2007 Kauer J. A, Malenka J. C. Synaptic plasticity and addiction. Nature Reviews Neuroscience. 2007; 8: 844–858. [Google Scholar]). Addiction-related learning is merely an extension of reward-based learning in this model, and it therefore involves similar transcription factors and neurotransmitters. For instance, DeltaFosB was found over a decade ago to be chronically elevated specifically in the medium spiny neurons of the nucleus accumbens in the brains of drug-addicted laboratory animals (Kelz et al., 1999 Kelz M. B, Chen J, Carlezon W. A, Whisler K, Gilden L, Beckmann A. M, et al. Expression of the transcription factor deltaFosB in the brain controls sensitivity to cocaine. Nature. 1999; 401: 272–276. [Google Scholar]). Subsequent studies have shown it to be elevated in these same cells in animals manifesting pathologic overconsumption of natural rewards, including food and sex (Nestler, 2005 Nestler E. J. Is there a common molecular pathway for addiction?. Nature Neuroscience. 2005; 9(11): 1445–1449. [Google Scholar]).

Supraphysiologic levels of DeltaFosB appear to portend hyperconsumptive states of natural addiction (Nestler, 2008 Nestler E. J. Transcriptional mechanisms of addiction: Role of DFosB. Philosophical Transactions of the Royal Society. 2008; 363: 3245–3256. [Google Scholar]). That DeltaFosB is not only a marker but also a facilitator of hyperconsumptive behavior (as a neuroplasticity enabler) has been well demonstrated. Two closely related mechanisms have been used to genetically manipulate DeltaFosB independent of behavioral variables. One involves producing lines of bitransgenic mice that selectively overexpress DeltaFosB specifically in the striatal reward areas, and the second involves the transfer of genes through adeno-associated viral vectors into adult animals, which then induce over- or underexpression of DeltaFosB. These genetically altered animals exhibit addictive hyperconsumptive behavior involving food (Olausson et al., 2006 Olausson P, Jentsch J. D, Tonrson N, Neve R. L, Nestler E. J, Tayor J. R. DeltaFosB in the nucleus accumbens regulates food reinforced instrumental behavior and motivation. Journal of Neuroscience. 2006; 26(36): 9196–9204. [Google Scholar]), wheel running (Werme et al., 2002 Werme M, Messer C, Olson L, Gilden L, Thoren P, Nestler E. J, et al. DeltaFosB regulates wheel running. Journal of Neuroscience. 2002; 22(18): 8133–8138. [Google Scholar]), and sex (Wallace et al., 2008 Wallace D. L, Vialou V, Rios L, Carle-Florence T. L, Chakravarty S, Arvind Kumar A, et al. The influence of DeltaFosB in the nucleus accumbens on natural reward-related behavior. Journal of Neuroscience. 2008; 28(4): 10272–19277. [Google Scholar]). For instance, when overexpression of DeltaFosB was imposed through these viral vectors in laboratory animals, they exhibited a supraphysiologic enhancement of sexual performance (Hedges, Chakravarty, Nestler, Meisel, 2009 Hedges V. L, Chakravarty S, Nestler E. J, Meisel R. L. Delta FosB overexpression in the nucleus accumbens enhances sexual reward in female Syrian hamsters. Genes Brain and Behavior. 2009; 8(4): 442–449. [Google Scholar]; Wallace et al., 2008 Wallace D. L, Vialou V, Rios L, Carle-Florence T. L, Chakravarty S, Arvind Kumar A, et al. The influence of DeltaFosB in the nucleus accumbens on natural reward-related behavior. Journal of Neuroscience. 2008; 28(4): 10272–19277. [Google Scholar]). Conversely, repression of DeltaFosB decreases performance (Pitchers et al., 2010 Pitchers K. K, Frohmader K. S, Vialou V, Mouzon E, Nestler E. J, Lehman M. N, et al. ΔFosB in the nucleus accumbens is critical for reinforcing effects of sexual reward. Genes Brain and Behavior. 2010; 9(7): 831–840. [Google Scholar]), thus confirming that it has a role in normal physiologic homeostasis.

It now appears that DeltaFosB is a molecular transcription switch that turns on other gene sets, which then mediate neuroplastic change in these neurons; in other words, they promote neuronal learning. DeltaFosB increases dendritic spine density in medium spiny neurons in the nucleus accumbens in addicted animals during extended periods of abstinence through stimulation of the protein Cdk5, thus becoming a bridge to more extended neuroplasticity (Bibb et al., 2001 Bibb J. A, Chen J, Taylor J. R, Svenningsson P, Nisha A, Snyder G. L, et al. Effects of chronic exposure to cocaine are regulated by neuronal protein Cdk5. Nature. 2001; 410(6826): 376–380. [Google Scholar]; Norrholm et al., 2003 Norrholm S. D, Bibb J. A, Nestler E. J, Ouimet C. C, Taylor J. R, Greengard P. Cocaine-induced proliferation of dendritic spines in nucleus accumbens is dependent on the activity of cyclin-dependent kinase-5. Neuroscience. 2003; 116: 19–22. [Google Scholar]). DeltaFosB has been shown to function in a positive feedback loop with Calcium/Calmodulin-Dependent Protein Kinase II to effect neuroplastic cellular responses in cocaine addiction. Significantly, this association was also demonstrated, for the first time, in human cocaine addiction (Robison et al., 2013 Robison A. J, Violou V, Mazei-Robison M, Feng J, Kourrich S, Collins M, etal. Behavioral and structural responses to chronic cocaine require a feedforward loop involving DeltaFosB and Calcium/Calmodulin-Dependent Protein Kinase II in the nucleus accumbens shell. Journal of Neuroscience. 2013; 33(10): 4295–4307. [Google Scholar]).

Recent evidence has demonstrated that DeltaFosB is critical to this dendritic plasticity through its effect on the mesolimbic reward system in both sexual and drug rewards, an effect that is mediated by the D1 dopamine receptor in the nucleus accumbens (Pitchers et al., 2013 Pitchers K. K, Vialou V, Nestler E. J, Laviolette S. R, Lehman M. N, Coolen L. M. Natural and drug rewards act on common neural plasticity mechanisms with DeltaFosB as a key mediator. Journal of Neuroscience. 2013; 33(8): 3434–3442. [Google Scholar]). Dopamine is critical in assigning salience to sexual cues (Berridge & Robinson, 1998 Berridge K. C, Robinson T. E. What is the role of dopamine in reward: Hedonic impact, reward learning, or incentive salience?. Brain Research Reviews. 1998; 28: 309–369. [Google Scholar]), and recent studies support a physiologic role in sexual function as well through its effect on and interaction with the hypothalamic oxytocinergic systems (Baskerville, Allard, Wayman, & Douglas., 2009 Baskerville T. A, Allard J, Wayman C, Douglas A. J. Dopamine oxytocin interactions in penile erection. European Journal of Neuroscience. 2009; 30(11): 2151–2164. [Google Scholar]; Succu et al., 2007 Succu S, Sanna F, Melis T, Boi T, Argiolas A, Melis M. R. Stimulation of dopamine receptors in the paraventricular nucleus of the hypothalamus of male rates induces penile erection and increases extracellular dopamine in the nucleus accumbens: Involvement of central oxytocin. Neuropharmacology. 2007; 52(3): 1034–1043. [Google Scholar]). This influence has been broadly conserved across phyla (Kleitz-Nelson, Dominguez, & Ball, 2010 Kleitz-Nelson H. K, Dominguez J. M, Ball G. F. Dopamine release in the medial preoptic area is related to hormonal action and sexual motivation. Behavioral Neuroscience. 2010; 124(6): 773–779. [Google Scholar]; Kleitz-Nelson, Dominguez, Cornil, & Ball, 2010 Kleitz-Nelson H. K, Dominguez J. M, Cornil C. A, Ball G. J. Is sexual motivation state linked to dopamine release in the medial proptic area?. Behavior Neuroscience. 2010; 124(2): 300–304. [Google Scholar], Pfaus, 2010 Pfaus J. G. Dopamine: Helping males copulate for at least 200 million years: Theoretical comment of Kleitz-Nelson et al. (2010). Behavioral Neuroscience. 2010; 124(6): 877–880. [Google Scholar]), ensuring that sex, which is essential to species survival, remains salient. Hypersexuality as a consequence of dopaminergic pharmacologic intervention is a known morbidity of such treatment, and it is related to ‘exaggerated cue-triggered incentive salience-based motivation’ (Politis et al., 2013 Politis M, Loane C, Wu K, O'Sullivan S. S, Woodhead Z, Kiferle L, etal. Neural response to visual sexual cues in dopamine treatment-linked hypersexuality in Parkinson's disease. Brain. 2013; 136(Pt. 2): 400–411. [Google Scholar]). Addiction, of course, can be described as disordered salience. Instead of wanting that which will enhance survival, the addicted are motivated to want even when it is clearly harmful, a neuroplastic process that recalibrates the hedonic set point.

We see this neuroplasticity at the cellular level through dendritic arborization and other cellular changes that provide a neuroplastic ‘scaffolding’ of sorts for new synapses to form. Severe craving states associated with subsequent satiation have produced these micromorphologic changes, as demonstrated by such diverse depletion–repletion models as cocaine (Robinson & Kolb, 1999 Robinson T. E, Kolb B. Alterations in the morphology of dendrites and dendritic spines in the nucleus accumbens and prefrontal cortex following repeated treatment with amphetamine of cocaine. European Journal of Neuroscience. 1999; 11: 1598–1604. [Google Scholar]), amphetamine (Li, Kolb, & Robinson, 2003 Li Y, Kolb B, Robinson T. E. The location of persistent amphetamine-induced changes in the density of dendritic spines on medium-spiny neurons in the nucleus accumbens and caudate-putamen. Neurospsychopharmacology. 2003; 28: 1082–1085. [Google Scholar]), salt (Roitman, Na, Anderson, Jones, & Berstein, 2002 Roitman M. F, Na E, Anderson G, Jones T. A, Berstein I. L. Induction of a salt appetite alters dendritic morphology in nucleus accumbens and sensitizes rats to amphetamine. Journal of Neuroscience. 2002; 22 (11): RC225:1–5. [Google Scholar]), and sex (Pitchers, Balfour et al., 2012 Pitchers K. K, Balfour M. E, Lehman M. N, Richtand N. M, Yu L, Coolen L. M. Neuroplasticity in the mesolimbic system induced by natural reward and subsequent reward abstinence. Biological Psychiatry. 2012; 67: 872–879. [Google Scholar]). Salt depletion–repletion craving models have been shown to robustly mobilize the same gene sets activated by cocaine models, and this mobilization is attenuated by dopamine antagonists, suggesting that drug addiction usurps ancient incentive pathways that are essential to survival (Liedtke et al., 2011 Liedtke W. B, McKinley M. J, Walker L. L, Zhang H, Pfenning A. R, Drago J, etal. Relation of addiction genes to hypothalamic gene changes subserving genesis and gratification of a classic instinct, sodium appetite. Proceedings of the National Academy of Sciences. 2011; 108(30): 12509–12514. [Google Scholar]).

Glutamate receptor trafficking is indicative of synaptic plasticity. Sex, as a powerful brain reward, has shown evidence of increasing silent synapses, which manifest as an increase in the NMDA–AMPA receptor ratio, a harbinger of subsequent synaptic plasticity and learning as these synapses are subsequently unsilenced, similar to what occurs with cocaine use (Pitchers, Schmid et al., 2012 Pitchers K. K, Schmid S, Sebastiano A. R, Wang X, Laviolette S. R, Lehman M. N, etal. Natural reward experience alters AMPA and NMDA receptor distribution and function in the nucleus accumbens. PloS One. 2012; 7 (4): e34700. [Google Scholar]). Specifically, this ratio change was immediate and long-lasting, and it was found in nucleus accumbens neurons afferent to the prefrontal cortex, an area that is important in mediating CSBs (Pitchers, Schmid et al., 2012 Pitchers K. K, Schmid S, Sebastiano A. R, Wang X, Laviolette S. R, Lehman M. N, etal. Natural reward experience alters AMPA and NMDA receptor distribution and function in the nucleus accumbens. PloS One. 2012; 7 (4): e34700. [Google Scholar]). In this, sex is unique among natural rewards, in that food reward did not cause this same persistent change in synaptic plasticity (Chen et al., 2008 Chen B. T, Bowers M. S, Martin M, Hopf F. W, Guillory A. M, Carelli R. M, etal. Cocaine but not natural reward self-administration nor passive cocaine infusion produces persistent LTP in the VTA. Neuron. 2008; 59: 288–297. [Google Scholar]). Critically, neuroplastic changes in both dendritic morphology and glutamate receptor trafficking were correlated with increased sexual experience and increased amphetamine sensitivity, another hallmark of addiction. Even after 28 days, when these changes receded, the sex-induced hypersensitivity to amphetamine persisted (Pitchers et al., 2013 Pitchers K. K, Vialou V, Nestler E. J, Laviolette S. R, Lehman M. N, Coolen L. M. Natural and drug rewards act on common neural plasticity mechanisms with DeltaFosB as a key mediator. Journal of Neuroscience. 2013; 33(8): 3434–3442. [Google Scholar]), further strengthening the evidence for natural addiction.

A few selected studies on sexual reward and DeltaFosB published after The Great Porn Experiment TEDx talk, and since the above review.

1) DeltaFosB: A Molecular Switch for Reward (2013) - Excerpts:

Such a prolonged induction of ΔFosB, within the brain's reward regions, has been implicated in animal models of drug addiction, with a wealth of evidence indicating that ΔFosB promotes reward and motivation and serves as a key mechanism of drug sensitization and increased drug self-administration. This has been validated in humans postmortem, with elevated ΔFosB levels seen in reward regions of the addicted brain….

These findings suggest that ΔFosB in this brain region sensitizes animals not only for drug rewards, but for natural rewards as well, and thereby drives a higher motivational state for rewards in general and could possibly contribute to syndromes of natural addiction…..

If this hypothesis is correct, it raises the interesting possibility that levels of ΔFosB in NAc or perhaps other brain regions could be used as a biomarker to assess the state of activation of an individual’s reward circuitry, as well as the degree to which an individual is “addicted,” both during the development of an addiction and its gradual waning during extended withdrawal or treatment. The use of ΔFosB as a marker of a state of addiction has been demonstrated in animal models. Adolescent animals show much greater induction of ΔFosB compared to older animals, consistent with their greater vulnerability for addiction.

2) Natural and Drug Rewards Act on Common Neural Plasticity Mechanisms with ΔFosB as a Key Mediator (2013) - This study examined the effects of sexual reward on DeltaFosB and the effects of DeltaFosB on sexual behavior and reward. The standard molecular changes known to occur with drug addiction were found to be the same as occur with sexual reward. Same circuits, same mechanisms, same cellular changes, same associated behaviors - with minor differences. Excerpts:

Drugs of abuse induce neuroplasticity in the natural reward pathway, specifically the nucleus accumbens (NAc), thereby causing development and expression of addictive behavior. Recent evidence suggests that natural rewards may cause similar changes in the NAc, suggesting that drugs may activate mechanisms of plasticity shared with natural rewards, and allowing for unique interplay between natural and drug rewards.

Together, these findings demonstrate that drugs of abuse and natural reward behaviors act on common molecular and cellular mechanisms of plasticity that control vulnerability to drug addiction, and that this increased vulnerability is mediated by ΔFosB and its downstream transcriptional targets.

Thus, natural [sexual] and drug rewards not only converge on the same neural pathway, they converge on the same molecular mediators (Nestler et al., 2001; Wallace et al., 2008; Hedges et al., 2009; Pitchers et al., 2010b), and likely in the same neurons in the NAc (Frohmader et al., 2010b), to influence the incentive salience and the “wanting” of both types of rewards (Berridge and Robinson, 1998).

3) Delta JunD overexpression in the nucleus accumbens prevents sexual reward in female Syrian hamsters (2013) - Excerpts:

Motivated behaviors, including sexual experience, activate the mesolimbic dopamine system and produce long-lasting molecular and structural changes in the nucleus accumbens. The transcription factor ΔFosB is hypothesized to partly mediate this experience-dependent plasticity.

We found that overexpression of ΔJunD prevented the formation of a conditioned place preference following repeated sexual experiences. These data, when coupled with our previous findings, suggest that ∆FosB is both necessary and sufficient for behavioral plasticity following sexual experience. Furthermore, these results contribute to an important and growing body of literature demonstrating the necessity of endogenous ΔFosB expression in the nucleus accumbens for adaptive responding to naturally rewarding stimuli.

4) Nucleus accumbens NMDA receptor activation regulates amphetamine cross-sensitization and deltaFosB expression following sexual experience in male rats (2015) - Excerpts:

Sexual experience in male rats followed by a period of abstinence causes sensitization to d-Amphetamine (Amph) reward, evidenced by an increased conditioned place preference (CPP) for low doses of Amph. Moreover, sexual experience induces neural plasticity within the nucleus accumbens (NAc), including induction of deltaFosB, which plays a key role in Amph reward cross-sensitization.

Together, these results provide evidence that NAc NMDA receptor activation during sexual behavior plays a key role in mating-induced cFos and deltaFosB expression and subsequent experience-induced cross-sensitization to Amphetamine reward.

6) Ventral Tegmental Area Dopamine Cell Activation during Male Rat Sexual Behavior Regulates Neuroplasticity and d-Amphetamine Cross-Sensitization following Sex Abstinence (2016) - Excerpts:

Drugs of abuse act on the neural pathways that mediate natural reward learning and memory. Exposure to natural reward behaviors can alter subsequent drug-related reward. Specifically, experience with sexual behavior, followed by a period of abstinence from sexual behavior, causes increased reward for amphetamine in male rats. This study demonstrates that activation of ventral tegmental area dopamine neurons during sexual experience regulates cross-sensitization of amphetamine reward. Finally, ventral tegmental area dopamine cell activation is essential for experience-induced neural adaptations in the nucleus accumbens, prefrontal cortex, and ventral tegmental area. These findings demonstrate a role of mesolimbic dopamine in the interaction between natural and drug rewards, and identify mesolimbic dopamine as a key mediator of changes in vulnerability for drug use after loss of natural reward.

Finally, it must be noted that critics of The Great Porn Experiment, such as Nicole Prause, Jim Pfaus, David Ley, and Marty Klein have all claimed that sexual arousal/orgasm is no different neurobiologically than other natural rewards (food, water). In this HuffPost article, Nicole Prause suggested that masturbating to porn and watching puppies play are neurologically equivalent.

I mention this here because Prause has stated that she has contacted TED several times to complain about The Great Porn Experiment. TED should be aware of the unsupported claims put forth by those claiming to be the real experts. The spurious claim that viewing puppies is no different neurologically from masturbating to porn was addressed by Don Hilton MD in this article: Correcting Misunderstandings About Neuroscience and Problematic Sexual Behaviors. The relevant excerpt:  

While playing with puppies might activate the reward system (unless you are a cat person), such activation doesn’t support the claim that all natural rewards are neurological equivalents. First, sexual arousal and orgasm induce far higher levels of dopamine and endogenous opioids than any other natural reward. Rat studies reveal that the dopamine levels occurring with sexual arousal equal those induced by the administration of morphine or nicotine.

Sexual arousal is also unique because it activates precisely the same reward system nerve cells as do addictive drugs.  In contrast, there’s only a small percentage of nerve-cell activation overlap between addictive drugs and natural rewards such as food or water. Not surprisingly, researchers have also established that the natural reward of food does not cause the same persistent change in synaptic plasticity as sexual activity (Chen et al., 2008).

However, this is not to say that gustatory reward cannot become addictive or disruptive to individuals and precipitate public health concerns, or cause brain changes in reward circuits. Any physician knows that obesity is a tremendous health concern consuming billions in medical costs, and dopamine receptor depletion in the brain’s reward center returns to more normal density with weight loss after gastric banding surgery. Also, the DNA transcripts which produce reward system proteins important in the craving states that are evoked with salt depletion/repletion are identical to those produced with drug craving (Leidke et al., 2011, PNAS).  A National Geographic article on this paper said drugs “hijack” these natural reward pathways, and this is true for all addiction, whether to poker, porn, or popcorn.

Addictive drugs not only hijack the precise nerve cells activated during sexual arousal, they co-opt the same learning mechanisms that evolved to make us desire sexual activity. Activation of the same nerve cells that make sexual arousal so compelling helps explain why meth, cocaine, and heroin can be so addictive. Also, both sex and drug use can induce transcription factor DeltaFosB, resulting in neuroplastic alterations that are nearly identical for both sexual conditioning and chronic use of drugs.

While far too complex to elucidate in detail, multiple temporary neurological and hormonal changes occur with orgasm that do not occur with any other natural rewards. These include decreased brain androgen receptors, increased estrogen receptors, increased hypothalamic enkephalins, and increased prolactin. For example, ejaculation mimics the effects of chronic heroin administration on reward system nerve cells (the ventral tegmental area, or VTA). Specifically, ejaculation temporarily shrinks the same dopamine producing nerve cells that shrink with chronic heroin use, leading to temporary down-regulation of dopamine in the reward center (nucleus accumbens).

A 2000 fMRI study compared brain activation using two different natural rewards, one of which was porn. Cocaine addicts and healthy controls viewed films of: 1) explicit sexual content, 2) outdoor nature scenes, and 3) individuals smoking crack cocaine. The results: cocaine addicts had nearly identical brain activation patterns when viewing porn and viewing cues related to their addiction. (Incidentally, both cocaine addicts and healthy controls had the same brain activation patterns for porn.) However, for both the addicts and controls, brain activation patterns when viewing nature scenes were completely different from the patterns when viewing for porn. In short, there are multiple biological reasons we experience an orgasm differently from playing with puppies or viewing sunsets.  Millions of adolescent boys and increasingly girls are not just watching puppies on the Internet, and Mindgeek knows that to make billions in ad revenues you name a site “Pornhub,” not “PuppyHub!”


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