Repeatedly viewing violent scenes in videogames could make aggression "more acceptable" in teenagers, a new US study suggests.
The National Institutes of Health study of 22 boys aged 14 to 17 found that showing dozens of violent clips in film, television or videogames appeared to blunt brain responses, reports the BBC.
Dr Jordan Grafman said it might make aggression feel more "acceptable".
"The implications of this include the idea that continued exposure to violent videos will make an adolescent less sensitive to violence, more accepting of violence, and more likely to commit aggressive acts since the emotional component associated with aggression is reduced and normally acts as a brake on aggressive behaviour," he said.
The conclusion was countered by Professor David Buckingham, Director of the Centre for the Study of Children, Youth and Media, who said, "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."
The study focused on a debate that has rages for years now: do violent videogames make those who experience them more violent?
So far, almost all studies have failed to find a conclusive answer.
This NIH study involved 60 violent scenes, mostly involving street brawling and fist fights. The violence was ranked "low", "mild" or "moderate", and there were no "extreme" scenes. The response of the boys as they watched the clips was measured in a number of ways.
The longer the boys watched the videos the less they responded to the violence within them. In particular, an area of the brain known as the lateral orbitofrontal cortex, thought to be involved in emotional processing, showed less activity to each clip as time went on.
"This debate has been going on since before we were all born," said Professor Buckingham. "In the 19th Century people were panicking about the effect of 'Penny Dreadfuls'.
"If we are truly interested in violence and aggression, rather than blaming the media for everything wrong in the world, we need to look at what motivates it in real life."
In March 2008, following the publication of her report investigating the effect of violence in the media on children, Dr Tanya Byron warned against holding games accountable for society's problems.
Byron said, "Let's stop blaming industry for things industry isn't responsible for, that's number one. "Number two, the industry has worked really positively with me. I do believe this industry does not intend to corrupt young people. Number three, I think there's a positive that adult games are created with adult content for adults to play."