A new study finds that men who watch a lot of pornography tend to have less gray matter volume as well as less activity in the region of the brain linked to rewards.

The German study, published in JAMA Psychiatry and which analyzed a relatively small sample, provides the first evidence which could lead to establishing a link between pornography consumption and brain size. However, it did not determine whether watching porn leads to the decreased volume and activity, or if people born with certain brain characteristics watch more porn.

The study’s researchers questioned 64 healthy men aged 21 to 45 about their porn watching habits. They also examined how their brains reacted to pornographic images and took images of their brains in order to measure volume.

The results also show that the brain region activated when people view sexual stimuli is less active in men who watch a lot of pornography. It also shows the part of the brain associated with processing rewards is smaller in men who view pornography more often.

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