COMMENTS

Published in JAMA Psychiatry (May, 2014), this was the first brain-scan study on porn users. Researchers found several brain changes, and those changes correlated with the amount of porn was consumed. The subjects were moderate porn users, not classified as addicted. In this study, experts at Germany’s Max Planck Institute found:

1) Higher hours per week/more years of porn viewing correlated with a reduction in grey matter in sections of the reward circuitry (striatum) involved in motivation and decision-making. Reduced grey matter in this reward-related region means fewer nerve connections. Fewer nerve connections here translates into sluggish reward activity, or a numbed pleasure response, often called desensitization. The researchers interpreted this as an indication of the effects of longer-term porn exposure. Lead author Simone Kühn said:

“That could mean that regular consumption of pornography more or less wears out your reward system.”

2) The nerve connections between the reward system and prefrontal cortex worsened with increased porn watching. As the study explained,

“Dysfunction of this circuitry has been related to inappropriate behavioral choices, such as drug seeking, regardless of the potential negative outcome.”

In short, this is evidence of an association between porn use and impaired impulse control.

3) The more porn used the less reward system activation when exposed to sexual images. A possible explanation is that heavy users eventually need more stimulation to fire up their reward circuitry. Desensitization, leading to tolerance, is common in all kinds of addictions. Said the study,

“This is in line with the hypothesis that intense exposure to pornographic stimuli results in a down-regulation of the natural neural response to sexual stimuli.”

Simone Kühn continued:

“We assume that subjects with a high porn consumption need increasing stimulation to receive the same amount of reward.“

Kühn says existing psychological, scientific literature suggests consumers of porn will seek material with novel and more extreme sex games:

“That would fit perfectly the hypothesis that their reward systems need growing stimulation.”

The above findings dismantle the two primary arguments put forth by porn addiction naysayers:

That porn addiction is simply “high sexual desire“. Reality: The heaviest porn users had the lowest responses to sexual images. That’s not high “sexual desire.” That compulsive porn use is driven by habituation, or becoming easily bored. While this is true, habituation is often defined as a fleeting effect not involving measurable alterations in the brain.

To sum up: More porn use correlated with less gray matter and reduced reward system activity (in the dorsal striatum) when viewing sexual images. More porn use also correlated with weakened connections between the seat of our willpower, the frontal cortex, and the reward system. Media coverage:

Press release from The Max Planck Institute

Study shows a connection between consumption and brain structure

Ever since pornography appeared on the Internet, it has become more accessible than ever before. This is reflected in pornography consumption, which is on the rise globally. But what effect does the frequent consumption of pornography have on the human brain? A joint study by the Max Planck Institute for Human Development and the Psychiatric University Hospital Charité at St Hedwig Hospital is looking at just that question.

Pornography is a social taboo. Few will admit to its use, yet the market is enormous. In pre-Internet societies, pornography often had to be procured secretly. Today it can be viewed discretely and directly on a home computer with just a few clicks. Pornography sites rank high among the list of most-visited websites in Germany, often attracting more visits than major media and retail sites.

But what effect does the consumption of pornographic material have on the human brain? Berlin-based researchers Simone Kühn and Jürgen Gallinat looked into the matter. The scientists studied 64 adult men aged 21 to 45. The subjects were first asked about their current consumption of pornography. For example: “Since when have you been using pornographic material?” and “For how many hours a week on average do you view it?” Then, with the help of magnetic resonance imaging, the researchers recorded brain structure and brain activities while the subjects were viewing pornographic images.

The evaluation found a connection between the number of hours the subjects spent viewing pornographic material per week and the overall volume of grey matter in their brains, with a negative correlation between pornography use and the volume of the striatum, an area of the brain that makes up part of the reward system. The more the subjects were exposed to pornography, the smaller the volume of their striatum. “This could mean that regular consumption of pornography dulls the reward system, as it were,” says Simone Kühn, lead author of the study and scientist in the developmental psychology research area at the Max Planck Institute for Human Development.

Moreover, while the subjects were viewing sexually stimulating images, the level of activity in the reward system was significantly lower in the brains of the frequent and regular users of pornography than in seldom and irregular users. “We therefore assume that subjects with high pornography consumption require ever stronger stimuli to reach the same reward level,” says Simone Kühn. This is consistent with the findings on the functional connectivity of the striatum to other brain areas: high pornography consumption was found to be associated with diminished communication between the reward area and the prefrontal cortex. The prefrontal cortex, together with the striatum, is involved in motivation and appears to control the reward-seeking drive.

The researchers believe that the findings on the connectivity between the striatum and other brain areas can be interpreted in two ways: either the decreased connectivity is a sign of experience-dependent neuronal plasticity, i.e. an effect of pornography consumption on the reward system, or alternatively, it could be a precondition that determines the level of pornography consumption. The researchers think that the first interpretation is the more likely explanation. “We assume that frequent pornography use leads to these changes. We’re planning follow-up studies to demonstrate this directly,” adds Jürgen Gallinat, co-author of the study and psychiatrist at the Psychiatric University Hospital Charité at St Hedwig Hospital.

UPDATE:

May, 2016. Kuhn & Gallinat published this review – Neurobiological Basis of Hypersexuality (2016). In the review Kuhn & Gallinat describe their 2014 fMRI study:

In a recent study by our group, we recruited healthy male participants and associated their self-reported hours spent with pornographic material with their fMRI response to sexual pictures as well as with their brain morphology (Kuhn & Gallinat, 2014). The more hours participants reported consuming pornography, the smaller the BOLD response in left putamen in response to sexual images. Moreover, we found that more hours spent watching pornography was associated with smaller gray matter volume in the striatum, more precisely in the right caudate reaching into the ventral putamen. We speculate that the brain structural volume deficit may reflect the results of tolerance after desensitization to sexual stimuli. The discrepancy between the results reported by Voon and colleagues could be due to the fact that our participants were recruited from the general population and were not diagnosed as suffering from hypersexuality. However, it may well be that still pictures of pornographic content (in contrast to videos as used in the study by Voon) may not satisfy today’s video porn viewers, as suggested by Love and colleagues (2015). In terms of functional connectivity, we found that participants who consumed more pornography showed less connectivity between the right caudate (where the volume was found to be smaller) and left dorsolateral prefrontal cortex (DLPFC). DLPFC is not only known to be involved in executive control functions but also known to be involved in cue reactivity to drugs. A specific disruption of functional connectivity between DLPFC and caudate has likewise been reported in heroin-addicted participants (Wang et al., 2013) which makes the neural correlates of pornography similar to those in drug addiction.

UPDATE:

The 2014 Cambridge fMRI study on porn addicts (Voon et al., 2014) explains the differences between these two studies in the discussion section:

In keeping with the literature on brain activity in healthy volunteers to explicit sexual stimuli activated regions, we show a similar network including the occipito-temporal and parietal cortices, insula, cingulate and orbitofrontal and inferior frontal cortices, pre-central gyrus, caudate, ventral striatum, pallidum, amygdala, substantia nigra and hypothalamus [13]–[19]. Longer duration of use of online explicit materials in healthy males has been shown to correlate with lower left putaminal activity to brief still explicit images suggesting a potential role of desensitization [23]. In contrast, this current study focuses on a pathological group with CSB characterized by difficulty with controlling use associated with negative consequences. Furthermore, this current study uses video clips as compared to brief still images. In healthy volunteers, viewing of erotic still images compared to video clips has a more limited activation pattern including hippocampus, amygdala and posterior temporal and parietal cortices [20] suggesting possible neural differences between the brief still images and the longer videos used in this current study. Furthermore, disorders of addiction such as cocaine use disorders have also been shown to be associated with enhanced attentional bias whereas recreational cocaine users have not been shown to have enhanced attentional bias [66] suggesting potential differences between recreational versus dependent users. As such, differences between studies may reflect differences in the population or task. Our study suggests that the brain responses to explicit online materials may differ between subjects with CSB as compared to healthy individuals who may be heavy users of explicit online materials but without the loss of control or association with negative consequences.

THE STUDY – Brain Structure and Functional Connectivity Associated With Pornography Consumption: The Brain on Porn

JAMA Psychiatry. Published online May 28, 2014. doi:10.1001/jamapsychiatry.2014.93

Full study in PDF form.

Simone Kühn, PhD1; Jürgen Gallinat, PhD2,3