Researchers found less gray matter in the brains of men who watched large amounts of sexually explicit material, according to a new study.
The research, which appeared Wednesday in the journal JAMA Psychiatry, could not determine if porn actually caused the brain to shrink however, and the authors called for additional study on the topic.
"Future studies should investigate the effects of pornography longitudinally or expose naive participants to pornography and investigate the causal effects over time," said researchers at the Max Planck Institute for Human Development in Berlin, Germany.
The institute recruited 64 male subjects aged 21-45, "with a broad range of pornography consumption."
The men were not told initially that the research was monitoring their brains on porn, rather that it was "a scientific study including magnetic resonance imaging (MRI) measurements."
The men were told during a later phone interview that questions about pornography would be part of the research, and none dropped out.
The men filled out surveys, describing how much porn they watched. Their responses averaged a little more than four hours per week.
Their brains were scanned with MRI technology while they were shown sexually explicit images from porn websites, along with non-sexual images of people exercising.
"Our findings indicated that gray matter volume of the right caudate of the striatum is smaller with higher pornography use," said the study.
Furthermore, when sexually explicit material was shown, the men's MRIs showed diminished function in a part of the brain that processes motivation.
But were men with smaller striatums seeking more porn, or did more porn make the brain smaller? Was it a consequence, or a precondition?
"Individuals with lower striatum volume may need more external stimulation to experience pleasure and might therefore experience pornography consumption as more rewarding, which may in turn lead to" more porn watching, said the authors, concluding that more study is needed.