A survey at Japan's Nihon University has revealed that
video games decrease brain activity in the brain regions for emotion and creativity. Activity does not recover, and heavy video game users were found to have trouble concentrating, managing anger and associating with friends. (Mind you, this is from the Mainichi, which appears to be a somewhat sensationalist tabloid.)
I tried to concentrate on reading the article, but then I got pissed off and locked myself in my room.