Of Rats, Voles, and Online Pornography Addiction


This article also appeared in Areo Magazine.

Rats in a Skinner Box

Rats wired up to electrodes, housed in an experimental Skinner box, continually press a button to give themselves powerful, pleasurable sensations. The rats go into a veritable lever-pushing frenzy, even when it means depriving themselves of food. Put the rat in a box where a tap of the lever releases cocaine, the same thing happens. They had to be unhooked from the apparatus to prevent death by self-starvation. In his book The Brain That Changes Itself, Dr Norman Doidge describes a study of men viewing pornography. The men, he wrote, looked “uncannily” like the rats pushing the levers. “Like the addicted rats the men were desperately seeking their next fix, clicking the mouse just as the rats pushed the lever.”

The majority of people who watch porn online do so recreationally, with little ill effect. Only a small group of people will become addicted and suffer serious consequences as a result. But, for that subset of users, online pornography use has been described as the crack cocaine of online addictions. Is such a comparison fair? Why does Doidge reference men only? Are men more addicted to pornography than women, and, if so, why? Why only some men?

To answer these questions, I look at similarities between drug use and porn addiction. I use what’s known as the dopamine hypothesis model—making links between neurobiology and theories from evolutionary biology. This might be termed a ‘hard deterministic’ perspective. Other models of pornography addiction take into account social and environmental factors, and I consider these elsewhere. To use a computer analogy, if social and environmental models constitute the software, in this article I focus on the hardware: the human brain, genes, and neurochemistry.


Are men more addicted than women?

There are two factors to consider here: first, the number of men versus women who watch pornography. Second, is the rate of problematic porn consumption  for men versus women. The studies I cite below refer to video pornography, not other types of online pornography, such as erotic literature. There are differences in how men and women consume pornography.  One major difference is that on average more men watch online porn, more women read it.

Numerous studies have tracked the number of men and women who watch porn. One study, which tracked porn use over several decades, found that twice as many men as women had watched an X-rated movie in any given year. The same study also found that the percentage increase in viewing by men was almost double that of women over a forty-year period.  Other studies have found men watch three times more pornography than women on a weekly or daily basis. Men are also more likely to be heavy users of porn.

Studies comparing rates of problematic porn use between men and women are rarer, but those that do exist show that rates of addiction are higher among men. One 2017 study found that 19% of male college students met the criteria for pornography addiction—only 4% of women met the same criteria. A separate 2017 study saw four times as many men as women self-identify as addicted. A 2011 study from Sweden found almost three times more men than women report issues with online porn use. Not only do men watch more porn, but rates of addiction for men are also higher; by between three to five times. But why?

A Tale of Two Voles

The prairie vole, a native of the American plains, is a pair-bonder. This means he chooses one partner and remains with her for life. He is also pro-social and—thanks to his penchant for hanging around—a good father. Compare him to his cousin, the meadow vole, with whom he shares the plains. The meadow vole, notoriously promosicuous, is in many ways his opposite. More given to a nest-hopping lifestyle, he is less social and not renowned for his fathering skills.

Researchers set out to discover what causes such different behavior and found a genetic variance: a difference in the allele RS3 334, related to the neurochemical vasopressin, a crucial ingredient in pair-bonding. For engaging in this pro-social behavior the prairie vole receives a neurochemical reward; namely a hit of vasopressin. This creates a positive feedback loop; more vasopressin encourages continued loyalty, which releases more vasopressin; ad infinitum.

The opposite is true for the meadow vole. Lacking vasopressin receptors, he is more inclined to promiscuity, is more anti-social, has less developed fathering skills etc.

RS3 334

Following this discovery, studies were conducted to see whether the same genetic variant had any influence on male sexual behavior in humans. The same variant was discovered to exist and a link to promiscuity was found. Men have either zero, one or two copies of the allele RS3 334. Men with zero copies are more likely to remain monogamous, while males with one copy have less likelihood of forming a strong bond with their partners. Males who have inherited two copies are more likely to stray and more at risk of divorce than other men. Meanwhile, women feel no affects of variants of the allele at all. This is not to say that women never stray. Not only might genes play a role when they cheat, but when women are promiscuous they are promiscuous in a different way.

Is RS3 334 – if implicated in extra-marital promiscuity – related to pornography addiction? This is a relatively new area of research and to date no pornography studies have been done controlling for the genetic variant. However, there is plenty of evidence to suggest a link exists. One 2015 study linked a lack of vasopressin receptors not just to cheating, but to a higher risk of displaying other symptoms of hypersexual disorder, including excessive use of pornography. The authors also noted the link between decreased vasopressin activity and an increase in dopamine activity in hypersexuality. This contrast is important because it marks another difference between the prairie and meadow voles. Whereas the neurocircuitry of the prairie vole contains more vasopressin receptors, the promiscuous meadow vole has more dopamine receptors.

What would happen if the opposite were true? Would regulation by a different neurochemical have an effect on either vole?

Curious to see if a difference in neurochemical regulation would produce a difference in behavior, researchers conducted two experiments. A team from the Emory University School of Medicine isolated the vasopressin gene and injected it into the meadow vole. The meadow voles gave up their amorous ways and turned instead to steadfast monogamy. To see what might happen to the prairie vole, a team from Florida State University triggered certain dopamine receptors in their brains, focusing on the D1 receptor. Tinkering with D1 caused the previously monogamous prairie vole to play the field. Researchers – amazed to discover cheating can be turned on or off like a switch – began to focus their attention on the role of dopamine in male sexuality.

Regulation by dopamine marks a difference between male and female neurobiology. On average, males are more left-brain dominant, more regulated by dopamine. Women tend to be more right-brain dominant, more regulated by serotonin. Dopamine is implicated, not just in promiscuity, but in a range of risk-taking activities—among them gambling, financial investment and drug addiction—traditionally male-dominated enterprises. This crude male-female divide should not lead us to ignore similarities between the genders, deny the effects of dopamine on women or downplay the delicate interplay of serotonin, oxytocin and vasopressin in determining male and female behavior. Rather, for those of us who are left-brain dominant, the role of dopamine at the extreme end of the neurochemical bell curve has implications for pornography addiction. Assume this caveat for subsequent male/female distinctions.

A Trip Through the Pleasure Centre

The mesolimbic dopaminergic pathway, more commonly known as the reward center, is located deep inside your brain. It comes as standard hardware in the brains of vertebrates. The reward center releases dopamine, a pleasure chemical, into your brain whenever you do something healthy, such as eat tasty food or exercise. The high you get from a dopamine rush makes you want to repeat that behavior again and again: this is so-called Pavlovian learning. The reward center’s job is to motivate you to repeatedly do those things that improve your health, thus improving your chances of survival. It’s termed Pavlovian because the brain learns to follow the same path: a neural pathway forms when the brain learns to associate a behavior with feelings of pleasure.

The problem is that the brain can be given a false signal, such as when taking addictive drugs—the brain can’t tell the difference between drug use and a real, healthy reward, and so it goes ahead and activates the reward center. In this case, the brain learns to follow the same path because the reward center has been tricked into thinking it is doing something healthy for the user. The presence of dopamine then activates cravings, which keep getting stronger until the user feels extremely motivated to keep pursuing more of the drug.

Addiction develops

Addictive drugs release up to ten times the amount of dopamine that natural rewards do. They do it faster and more reliably. Over time, the brain responds by producing less dopamine (or by eliminating dopamine receptors), resulting in a lessened impact on the reward center. When this happens, the user has to take in more of the substance to obtain the same dopamine release. In other words, they’ve built up a tolerance, and in continuing to seek out the behavior—in following the same neural pathway— addiction develops. An interesting correlate in terms of male/female differences is that the ratio for substance abuse is similar to the ratio for pornography addiction: about four to one.

The reward center also influences sexual behavior, sex being – for the most part – a healthy activity. The same mechanisms are used to reinforce behavior, not just for sexual pleasure but in order to fulfill the genetic imperative: to spread our genes as far as possible. To ensure as diverse a gene pool as possible, sex adds another ingredient to the mix: novelty. Scientists have long known that sexual interest and performance increases simply by introducing something new—such as a different sexual position, a toy, or a change of partner.

Morton’s study

Research by Heather Morton on partner familiarity showed that sexual arousal and desire decrease in response to partner familiarity and increase in response to partner novelty. The longer you’re with the same partner, doing the same thing, the greater the likelihood attraction will fade. However, by introducing something novel to the sexual aspect of the relationship, desire can be reignited. When dopaminergic tolerance builds up between partners, novelty can give a flagging sexual relationship a welcome boost because the brain responds to novel sexual stimuli by pumping out more of the good stuff.

According to Morton’s familiarity research, this effect of novelty is greater on men. She believes that the cause of the gender novelty gap lies in the differing sexual strategies of men and women. The different costs of child birth and child-rearing for men and women caused us to evolve different sexual strategies. On average, more men than women developed promiscuous behaviour. While the Pill and abortion may prove evolutionary game changers longer-term, fifty years of their wide availability have not seen much change across a range of evolutionary measures, including promiscuity.

The Coolidge Effect

In her paper, Morton refers to a phenomenon underpinning the promiscuous strategy: the Coolidge effect. The Coolidge effect is a biological phenomenon whereby the males of most species renew their sexual interest whenever a new female is introduced, even after having had sex with previous (but still available) sexual partners. One way to describe the Coolidge effect is as a measure of the effect of novelty on the promiscuity of males of (almost) all species. Pair-bonders like the prairie vole score low in Coolidge effect studies, while promiscuous species like the meadow vole score highly.

The persistent seeking of novelty gives the meadow vole his high score—his lack of interest in sex toys and new positions notwithstanding. The benefit of the Coolidge effect from an evolutionary perspective is that the male has more energy to fertilize multiple females. Spreading genes is nature’s number one priority and the promiscuous strategy maximizes reproduction. The more women a male sleeps with, the more likely his DNA manifests in the future. This is a variant on evolutionary game theory.

Have there been Coolidge effect studies on men? Kind of. Researchers carry out most Coolidge effect studies on non-human species. A typical experiment involves putting a male rat in a cage with four or five females in heat. The scientists leave the male rat until he’s exhausted – his dopamine levels depleted – then measure the effects when a new female is introduced. Conducting this form of research with human subjects could present some difficulties for ethics committees. Instead, Coolidge effect studies on men are done using pornographic images.

Higher arousal

In these studies, men divide into two groups. The first group watches the same sexual images continually, the second group sees a variety of different sexual images. The men shown the constant sexual images showed less arousal over time, just like the men in Morton’s familiarity study. Meanwhile, those exposed to novel images maintained significantly higher levels of arousal. In the second group, researchers  noted faster ejaculations, and found more sperm and erection activity. These findings compared to the rats in the Coolidge studies.

A separate study found that men exposed to novel images produced higher volumes of sperm. Not only that but they produced sperm that is more motile; that is more likely to reach its target. The evolutionary advantage of such a mechanism is obvious. More sexual activity and more sperm hitting home means a more diverse gene pool. Less obvious is the effect modern technology can have on a reptilian brain process through the Coolidge effect.

The dopamine effect developed over millions of years, at a time in our evolution when sightings of females were much rarer. In evolutionary terms, a ‘novelty trip switch’ is useful when making a lonely trek across the African savannah. But what happens if you plug the modern male brain into a pornified matrix and suddenly new partners appear everywhere?

Novelty and Online Porn

The way we encounter pornography has radically changed. Previously, everybody had to pay for pornography. These days, however, high-definition streams are unlimited; free and widely available. The advent of aggregate sites like Pornhub has allowed users to upload and categorize videos. These sites provide a constant stream of Technicolour erotic images delivered at high speed, fresh to your optic cables, 24 hours a day. Before a user becomes bored, he clicks on an even more stimulating, hard-core link than before. As online pornography has developed, it has become easier to seek out new material. Not only has video pornography proven significantly more arousing than other forms of pornography, or even fantasy, but the ability to self-select material makes online pornography even more arousing than pre-selected collections.

What’s true of the real-life relationships in Morton’s study is also true of the pornography addict. When his dopamine levels are flagging, novelty will get him going again. And, with online pornography, it’s almost impossible to settle for habituation. A user can search not only for a different partner, but for a completely different genre of pornography. The dopamine depleted individual can progress to more explicit, graphic pornography in order to maintain a high level of excitement. Online, where the variety of fantasy is endless, novelty is only ever a click away.

Evolutionary superstimulus

Pornography gives us an opportunity to seek out a novel partner when our fertilization job appears to be over As soon as someone has fertilized an apparently willing partner—or even just the image of one—there is a neurochemical deflation. In order to get a fresh hit of dopamine, the user hunts around for a novel fertilization opportunity and the cycle continues. For the casual user, the dopamine download can be invigorating, but for the addict it soon becomes debilitating. For these users, online pornography provides a superstimulus, an exaggerated simulation of an evolutionarily advantageous mechanism. It is the Coolidge effect on steroids. Like Doidge’s rats they end up clicking incessantly, in search of a jolt of pleasure.

Is the addict forever doomed by his neurobiology? Not necessarily. For the voles, the genetic differences aren’t absolute. Not all prairie voles remain faithful—some stray—and not all meadow voles are promiscuous. Similarly, not all men with extra copies of the RS3 334 allele cheat. Nor do all men with zero copies remain loyal. Environmental factors—both nurture and epigenetics—matter in whether or not genetic variants are acted upon. This raises the wider question as to how much of our environment and culture is informed by genetics? To what extent does our culture causes genes to switch on or off? But those are questions beyond the scope of this article.

Hardware versus software

I researched this article to inform myself, as a therapist, as to how to treat pornography addiction. While social and cultural factors -software issues – are always concerns in psychotherapy, it is useful to know what hardware issues might be taking place. It is possible to change neural pathways, adopt dopamine homeostasis strategies,  and remove environmental cues. For example, a 2015 neuroimaging study found that pornography addicts experience a dopamine surge as a response to erotic cues. That is to say the place, setting and associated rituals of their pornography viewing habits neurologically prime them for action. Such knowledge is useful, and has obvious treatment implications.

Both in terms of understanding this issue and how best to treat it, dopamine and neurochemistry matter.

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Posted in News on 15th February 2019
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