Men who report watching a lot of pornography tend to have less volume and activity in regions of the brain linked to rewards and motivation, says a new German study.
The study, published in JAMA Psychiatry, can't say watching porn caused the decrease in brain matter and activity, however.
It's not clear, for example, whether watching porn leads to brain changes or whether people born with certain brain types watch more porn, said Simone Kühn, the study's lead author from the Max Planck Institute for Human Development in Berlin, in an email.
Brain size and activity
"Unfortunately we cannot answer this question based on the results of the present study," Kühn said.
But, she noted, the results provide the first evidence for a link between pornography consumption and reductions in brain size and brain activity in response to sexual stimuli.
For the study, she and her colleague Jurgen Gallinat from Charite University, also in Berlin, recruited 64 healthy men between the ages of 21 and 45 years and asked them questions about their porn-watching habits. They also took images of the men's brains to measure volume and to see how their brains reacted to pornographic pictures.
"We found that the volume of the so-called striatum, a brain region that has been associated with reward processing and motivated behaviour was smaller the more pornography consumption the participants reported," Kühn said.
"Moreover we found that another brain region, that is also part of the striatum that is active when people see sexual stimuli, shows less activation the more pornography participants consumed," she added.
What's more, the researchers found that the connection between the striatum and prefrontal cortex, which is the outer layer of the brain associated with behaviour and decision making, worsened with increased porn watching.
Because the study can't prove that porn caused the changes to the brain, Kühn said it's not possible to say whether watching porn is actually harmful.
"Everything is going to be bad in excess and it's probably not terrible in moderation," Dr Gregory Tau of the Columbia University/New York State Psychiatric Institute in New York said.
Tau, who was not involved with the study, agreed that more research should be done in this area and that longer studies would be need to find out if porn leads to brain changes.
"It is possible that there are individuals with a certain kind of brain that are more susceptible to these kinds of behaviours," he said. "Or, it's possible it's the excessive use (of porn) that's perpetuating itself to causing brain changes. Or, it could be both."
Kühn said other behaviours, such as driving a taxi, are linked to changes to brain size and functioning.
"Basically everything that people do very frequently can shape their brain structure and function," she said.
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