According to a medical study on Reuters.com , there appears to be a possible link between violent video games and aggressive behavior.
Headed by Indiana University School of Medicine's Dr. Vincent Mathews, the study examined 44 youths between the ages of 13 and 17 (none of whom had any history of emotional issues or mental disease), and they were split into two groups to play two very different games: Medal of Honor: Frontline and Need for Speed: Underground . They used an MRI to track visible changes in brain activity during the gaming process.
Upon completion of the experiment, the 22 who had played MoH showed increased activity in the areas of emotional arousal and decreased activity in the areas of control and focus.
"What we showed is there is an increase in emotional arousal," said Dr. Mathews. "The fight or flight response is activated after playing a violent videogame."
After playing, the kids were asked to complete a series of tasks requiring concentration. Evidently, those who played NFS had an easier time with these tasks, although we don't have the details regarding this part of the testing.
These results were presented at a meeting of the Radiological Society of North America, but of course, they don't necessarily prove that violent video games invariably lead to violent behavior. However, Dr. Mathews does plan to conduct further studies and experiments concerning any long-term effects violent games may have on the brain.