Playing a video game triggers the same violent responses in the brain as actual aggression, researchers claim.
The men studied all played violent games regularly
A team from the University of Aachen, Germany, asked men to play a game which required them to kill terrorists in order to rescue hostages.
They found brain mapping scans showed the same kind of activity as when people imagine being violent themselves, New Scientist reports.
Game players' may be more "primed" for aggression, experts warn.
The study, presented to the Organisation for Human Brain Mapping Annual Meeting in Toronto, Canada, follows on from other research which showed people who played violent computer games reported high levels of aggression and to have committed assaults and robberies.
The German team studied 13 men aged between 18 and 26, who played games for an average of two hours a day.
They asked the men to play a violent game while their brain activity was monitored using magnetic resonance imaging (fMRI) scanning.
The researchers monitored the game scene by scene, and watched how brain activity changed during violent interactions and calmer interludes.
It was found that, when violence was imminent, the cognitive - information processing - parts of the brain became more active.
During a fight in the game, parts of the brain which deal with emotion, including the amygdala and the anterior cingulate cortex, were shut down.
The same pattern has been seen in brain scans of people during acts of imagined aggression.
Dr Klaus Mathiak, who led the research, said since it was impossible to scan the brains of people involved in actual fights, this was the closest researchers could get to seeing what was happening in people's brains.
Dr Niels Birbaumer, from the University of Tubingen in Germany, suggested playing games regularly would strengthen certain circuits in the brain, and a regular player faced with a real life violent situation may be more likely to react aggressively.
But Jeffrey Fagan, a violence expert from Columbia University in New York, said the link between the brain and violence was complex.
He said: "The frontal lobe functions associated with violence have more to do with restraint than the arousal to action".
And Dr Guy Cumberbatch, head of the independent Communications Research Group in the UK, said: "If the findings in this study were the same as when people responded to imaginary situations, why is it any different to seeing violence in films or at the theatre?
"The problem is, it's very much a witch-hunt in relation to video games."
He added: "The instinct to punch someone on the nose is pretty basic. I don't think it is influenced in any way by playing these games."