Many studies have concluded that people who play violent video games are more aggressive, more likely to commit violent crimes, and less likely to help others. But critics argue these correlations merely prove that violent people gravitate towards violent games, not that games can change behaviour.

Now psychologist Bruce Bartholow from the University of Missouri-Columbia and colleagues have found that people who play violent video games show diminished brain responses to images of real-life violence, such as gun attacks, but not to other emotionally disturbing pictures, such as those of dead animals, or sick children. And the reduction in response is correlated with aggressive behaviour.

he brain activity they measured, called the P300 response, is a characteristic signal seen in an EEG.

(electroencephalogram) recording of brain waves as we register an image. The P300 reflects an evaluation of the emotional content of an image says Bartholow, being larger if people are surprised or disturbed by an image, or if something is novel.

Violent scenes

The team recruited 39 experienced gamers, and used questionnaires to assess the amount of violent games they played. They then showed them real-life images, mostly of neutral scenes, but interspersed with violent or negative (but non-violent) scenes, while recording EEGs.

In subjects with the most experience of violent games, the P300 response to the violent images was smaller and delayed. �People who play a lot of violent video games didn�t see them as much different from neutral,� says Bartholow. They become desensitised. However, their responses are still normal for the non-violent negative scenes.

This may not be surprising - video games have been used to desensitise soldiers to scenes of war. But when the players were subsequently given the opportunity to �punish� a fake opponent in another game, those with the greatest reduction in P300 brain responses meted out the most severe punishments.

Even when the team controlled for the subjects� natural hostility, assessed by standard questionnaires, the violent games experience and P300 response were still strongly correlated with aggressiveness. �As far as I�m aware, this is the first study to show that exposure to violent games has effects on the brain that predict aggressive behaviour,� says Bartholow.

Real-life aggression

But the study has failed to convince some critics. �We habituate to any kind of stimulus,� says Jonathan Freedman, a psychologist from the University of Toronto, Canada, who has prepared several government-level reports on media and games violence. �All we are really getting is desensitisation to images. There�s no way to show that this relates to real-life aggression.�

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

Other researchers are more concerned. Craig Anderson of Iowa State University in Ames, who has studied the effect, says: �These brain studies corroborate the many behavioural and cognitive studies showing that violent video games lead to increases in aggression.�

The work will appear early in 2006 in the Journal of Experimental Social Psychology.

NewScientist.com news service
Helen Phillips

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