BERLIN – Frequent porn viewing may be associated with smaller brains in males, specifically in the areas of the brain linked to rewards and motivation. So says a new German study published in the American Medical Association journal JAMA Psychiatry.

The study did not find that watching porn diminishes male brain size or that males with smaller brains watch more porn — only that the two conditions may be related somehow.

“Unfortunately we cannot answer this question [of causality] based on the results of the present study,” Simone Kühn, the study’s lead author and a senior researcher at the Max Planck Institute for Human Development in Berlin, told Reuters.

Researchers studied 64 healthy men between the ages of 21 and 45, asking the men about their porn-watching habits. The researchers also electronically measured the size of the men’s brains and performed real-time scans while the men watched porn.

“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,” said Kühn. “Moreover, we found that another brain region — also part of the striatum that is active when people see sexual stimuli — shows less activation the more pornography participants consumed.”

Kühn and her colleagues concluded increased porn viewing appears to be associated with poor connections between the striatum and the prefrontal cortex. That’s the area of the brain believed to govern behavior and decision-making, as in deciding how much porn one should consume on a daily basis.

Kühn et al stopped short of drawing a causal relationship, however. In fact, the researchers noted, having poor intra-brain connections and smaller brain size to begin with might be “a precondition that makes pornography consumption more rewarding.”