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Commonsense explanations of neuroscience

Have We Discovered a Hidden Danger of Pornography?

A new study gets a lot of attention, but what does it mean?

Neuroscience has just peaked or bottomed out—which one is not yet clear.

One of our most prestigious journals, JAMA Psychiatry, has just published an article with the subtitle, “The Brain on Porn.” With such a sexy lead-in, it's no wonder that the findings quickly got taken out of context in the mass media. Within a few hours of the article appearing on the journal’s website, at least one eager journalist concluded that porn must be bad for your brain.

The true story is more complicated—but at least as interesting.

Here’s what happened: German neuroscientists Simone Kuhn, from the Max Planck Institute, and Jurgen Galinat, from Charite University Medicine in Berlin, scanned the brains of 64 healthy males. They also asked each of them how much pornography they watched in the average week, and how much they had watched across their entire lives.

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Why would psychiatrists care how much porn someone watched? As Kuhn and Galinat point out, the internet has given rise to an instant, cheap, and anonymous way to consume pornography, and subsequently, according to multiple reports, people have started watching more of it. Two thirds of adult males in the United States, and a little under half of women, watch porn at least once every month, according to one recent survey. Even monkeys do it: In another, now-famous recent study, male macaques gave up juice to see photos of female macaque bottoms.

Surely watching all that porn affects our brains somehow.  

Kuhn and Galinat’s evidence suggests that it might: The men who had watched more porn had smaller volume in the striatum, a region of the brain’s reward network. We know that when people receive a little money, their striatum activates a little, and when they receive a lot of money, their striatum activates a lot. The men who watched the most porn also had less activity in the striatum when viewing pictures of naked women. Since porn is, presumably, rewarding, the link between striatum size and time watching porn could mean that repeated exposure dulls the reward circuitry’s response to pleasure.

There was also a relationship between general internet use and time watching porn. The most voracious porn consumers also spent more time surfing the web than others. Could the relationship between brain volume and porn consumption simply reflect more time spent online? Kuhn and Galinat ran their analysis again to find out. And, sure enough, even when controlling for overall internet use, time watching pornography was still significantly related to striatum size. So it wasn’t just that porn consumers spent more time online; something specific about watching porn was related to striatum size.

What we do not know is whether this structural brain difference is, as Kuhn and Galinat write in their paper, "a precondition rather than a consequence of frequent pornography consumption.” In other words, it may be that men with a smaller striatum watch more porn in the first place. Since the study volunteers were only scanned once, we can’t answer questions about how consuming pornography changes the brain. We just know that there’s a relationship.

We also can’t tell how honest the men in the study were. The authors stressed to the men that their responses would be anonymous. But there could be a relationship between striatum size and a tendency to exaggerate that went undetected.

What this study does show is a relationship between brain volume and time spent watching porn. To truly find out how time watching porn affects the brain, we would need to follow the same individuals for a long period of time, to see if watching porn directly changes brain volume. The authors propose that we could "expose naive participants to pornography and investigate the causal effects over time."

Their idea leads me to one conclusion: it sounds like an interesting laboratory. 

 

Image credit: ERLC

Joshua Gowin, Ph.D., earned his doctorate in behavioral neuroscience at the University of Texas Health Science Center in Houston.

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