Video games accounted for $10 billion in sales in the United States last year, but there is growing concern about the effects the games may have on those who play them.

In the study, Mathews’s team randomly assigned 44 adolescents to play either a violent video game or a nonviolent video game for 30 minutes. They then had the adolescents undergo functional MRI (fMRI) brain scans while performing tasks that measured concentration and inhibition. fMRI measures real-time changes that occur when the brain is active.

The Indiana group found that, compared to children who weren’t playing a violent video game, kids who played these games had more activation in the amygdala, a brain area closely linked to emotional arousal.

At the same time, their brains showed a reduced activation in prefrontal brain areas involved in inhibition, concentration and self-control.

“These findings raise concern that these types of video games are having some sort of effect on the brain and likely an effect on behavior as well,” Mathews said.

“This is early evidence for a biological change supporting other research on violent video games,” added David S. Bickham, a research scientist at the Center on Media and Child Health at the Harvard School of Public Health in Boston. “This is a first step in this kind of research, but it isn’t conclusive,” he said.

The research is opening up new areas in understanding the process of how violent media results in negative and aggressive social behaviors, Bickham said.

Bickham said parents need to be vigilant regarding the media they are letting into their homes, since children learn from all media they encounter. “This is more evidence that violent media can lead to aggressive and negative behaviors,” he said. There’s more on media violence and children at the American Academy of Pediatrics.