Science Daily reports a bit of evidence that watching violent programs may not be benign:
Researchers at Columbia University Medical Center’s Functional Magnetic Resonance Imaging (fMRI) Research Center have shown that watching violent programs can cause parts of your brain that suppress aggressive behaviors to become less active.
“Our findings demonstrate for the first time that watching media depictions of violence does influence processing in parts of the brain that control behaviors like aggression. This is an important finding, and further research should examine very closely how these changes affect real-life behavior.”
What were the depictions of violence?
The violent stimuli depicted acts of physical violence perpetrated by one human on another without mitigating or unrealistic elements; in general, these contained shootings, stabbings, and other kinds of physical assault.
The source article doesn’t say but I suspect playing violent video games would elicit the same results. Evaluating this would be an interesting follow up study.
Here is the original research article.