University of Michigan has done a research on the effect of violent video games to the players. Very interesting result indeed:

“Playing violent video games changes brain function and desensitizes chronic players to violence, a new study shows.

"It's already well known that playing violent video games increases aggressive behavior and decreases helping behavior," said University of Michigan researcher Brad Bushman. "But this study is the first to link exposure to violent video games with a diminished reaction to violent images."

Forthcoming in the Journal of Experimental Social Psychology, the study was conducted by Bruce Bartholow, an assistant professor of psychology at the University of Missouri-Columbia, Marc Sestir at the University of North Carolina at Chapel Hill, and Bushman, a U-M professor of psychology and communications studies and a faculty associate at the U-M Institute for Social Research (ISR)…”

Read the full article [here].