A U.S. study suggests that repeated exposure to violent scenes in movies, television shows, or video games, can make teenage males more aggressive.

Researchers at the National Institutes of Health in Bethesda, Md., studied the brain responses of 22 boys aged 14 to 17 as they watched violent video clips, mostly involving street fights, the BBC reported.

The violence in the clips was ranked low, mild, or moderate, and none of the subjects were shown videos deemed to be extreme.

Scientists found that the longer the boys watched the clips, especially the mild or moderate ones, the less they responded to the violence they were witnessing.

Dr. Jordan Grafman, the study's lead author, said the results suggest that seeing violent scenes make adolescent males less sensitive to violence, and make them more likely to commit "aggressive acts since the emotional component associated with aggression is reduced and normally acts as a brake on aggressive behaviour."

However, David Buckingham, the director of the Centre for the Study of Children, Youth and Media, disputed the study's implications, saying that violence was a "social problem" with many complex factors and not simply a matter of examining the brain.

"The suggestion is that, over a period of time, people can develop a kind of tolerance to these images -- but another word for that is just boredom," Buckingham told the BBC.

Do you think exposure to violent media makes teenage males more aggressive? If you have younger male children, do you try to limit their access to violent media?