If your teenager's holiday haul includes “Medal of Honor,” “Call of Duty,” “Gears of War,” or even, perhaps, “Left Behind: Eternal Forces,” be prepared. A new study by Indiana University School of Medicine researchers indicates that violent video games have lingering effects on the brains of adolescents who play them.

Using the brain-scanning technology called functional magnetic resonance imaging (fMRI), Vincent Mathews, professor of radiology at the IU School of Medicine, and colleagues compared the brain functions of two groups of teens--one group played a violent “first-person shooter” video game for 30 minutes, while the other played an exciting, but nonviolent, car-chase game. Following the violent video game play, the fMRI study showed that the teenagers' brains had increased activation in the area associated with emotional arousal and the “fight-or-flight” response. They showed less activation in the prefrontal portions of the brain associated with planning, focus, and self-control.

“During tasks requiring concentration and processing of emotional stimuli,” Mathews says, “the adolescents who played the violent video game showed distinct differences in brain activation.” Mathews presented his findings in November at the annual meeting of the Radiological Society of North America. William Kronenberger, associate professor of psychology in the IU School of Medicine Department of Psychiatry also participated in the study, along with School of Medicine scientists Yang Wang, Andrew Kalnin, Kristine Mosier, and David Dunn.

Video games are huge business in the United States, with more than $10 billion in annual revenue, according to the Entertainment Software Association (ESA). Not surprisingly, there is considerable debate about the impact of video games on youth violence—the ESA refutes the connection on its Web site ( www.theesa.com ) with various statistics and research findings.

Mathews acknowledges that his study focused only on short-term effects so it doesn't shed light on whether the video game brain change is long-term or even permanent, nor does it explore whether the change in brain function translates into more violent behavior. He is planning new studies to better understand the duration and nature of the relationship between video game violence and brain function.

Meanwhile, “parents should be aware that there are at least short-term effects on brain functioning,” Mathews said in an online Newsweek interview at MSNBC.com. “The fact that we're showing this should raise concern that exposure could result in some longer-term changes. Parents need to be aware of this, and make their own decisions. The one thing they should not do is not pay attention.”