The brain's P300 response, reflects an evaluation of the emotional content of an image. In subjects with the most experience playing violent games, the P300 response to the violent images was smaller and delayed.

Psychologist Bruce Bartholow from the University of Missouri-Columbia and his colleagues found that people who play violent video games show diminished brain responses to images of real-life violence but not to other emotionally disturbing pictures, such as those of dead animals, or sick children, the New Scientist reported.

The study, which will appear in the Journal of Experimental Social Psychology, showed that the reduction in response is correlated with aggressive behavior.

No More Hockey?

The brain activity they measured, called the P300 response, reflects an evaluation of the emotional content of an image, Bartholow said.

In subjects with the most experience playing violent games, the P300 response to the violent images was smaller and delayed.

Jonathan Freedman, a psychologist from the University of Toronto, Canada, was critical of the study, saying: All we are really getting is desensitization to images. There's no way to show that this relates to real-life aggression.

He said stopping people playing violent video games would be like preventing them from playing sports such as football or hockey.