A new study shows that brains of men who frequently watch sexually explicit content have less gray matter. However, researchers were not able to determine if porn is the real cause of the brain reduction.

The study is the first to link porn and shrinkage in brain activity and size. Its goal is to find out whether frequent porn use is linked with the frontostriatal network, which is responsible for functions including memory, decision-making and attention.

It involved 64 male subjects aged 21 to 45 who reported the hours they view sexually explicit material every week. Porn consumption was linked to task-related activation, functional resting-state connectivity and neural structure.  

The participants answered surveys and described how much pornography they watched. The response was an average of over four hours per week. The brains of the participants were scanned using MRI (magnetic resonance imaging) technology as they watched sexually explicit content from pornographic websites as well as non-sexual photos of people doing exercise. Noticeable differences in participants who regularly watched sexual images or videos compared with those who abstained.

The findings showed that gray matter volume of the striatum's right caudate was smaller with higher volume of porn use.

"We found that the volume of the so-called striatum, a brain region that has been associated with reward processing and motivated behavior, was smaller the more pornography consumption the participants reported," lead author Simone 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."

The study also shows that the striatum is connected with the prefrontal cortex, the outer layer of the brain linked with decision-making and behavior.

However, other researchers said that porn consumed moderately was likely not damaging. Other behaviors including driving a cab are also associated with brain functioning and size changes. Things that people do often can shape their brain function and structure. Some people already have smaller striatums and are more likely to watch porn. People with lower striatum volume need more outside stimulation to experience pleasure, which may lead to more porn consumption. It is not determined whether viewing of pornography leads to changes in the brain or whether people who have these types of brain are more likely to watch porn.

The study has not determined the answer and more research is needed to understand the subject better. It was published in JAMA Psychiatry.