SAN DIEGO, CALIFORNIA—Why do teens—especially adolescent males—commit crimes more frequently than adults? One explanation may be that as a group, teenagers react more impulsively to threatening situations than do children or adults, likely because their brains have to work harder to rein in their behavior, a research team reported here yesterday at the Society for Neuroscience meeting.

Whether it's driving too fast on a slick road or experimenting with drugs, teenagers have a reputation for courting danger that is often attributed to immaturity or poor decision-making. If immaturity or lack of judgment were the only problem, however, one would expect that children, whose brains are at an even earlier stage of development, would have an equal or greater penchant for risk-taking, says Kristina Caudle, a neuroscientist at the Weill Cornell Medical College in New York City who led the study. But younger children tend to be more cautious than teenagers, suggesting that there is something unique about adolescent brain development that lures them to danger, she says.

It's hard to generalize about teenage impulsivity, because some adolescents clearly have more self-control than many adults, says principal investigator B. J. Casey, a neuroscientist. Still, a growing body of evidence suggests that, in general, teens specifically struggle to keep their cool in social situations, she says. Because many crimes committed during adolescence involve emotionally fraught social situations, such as conflict, Caudle and colleagues decided to test whether teens perform badly on a common impulsivity task when faced with social cues of threat. They recruited 83 people, ranging in age from 6 to 29, to perform a simple "Go/No-Go" task, in which they watched a series of faces making neutral or threatening facial expressions flicker past on a computer screen. Each time the participants saw a neutral face, they were instructed to hit a button. They were also told to hold back from pressing the button when they saw a threatening face. As the participants performed the task, the researchers monitored their brain activity with functional magnetic resonance imaging.

On the whole, teenagers made about 15% more errors than adults and children when attempting to stop themselves from pressing the button when they saw the threatening facial expression, the team reports. Males performed worse than females, suggesting a sex difference that fits with the disproportionate number of crimes that male teens commit, Caudle says. Those adolescents who did manage to restrain themselves showed significantly higher activity in a brain region called the ventromedial prefrontal cortex (vmPFC), which is involved in top-down control of behavior. "You could think of it as the brake," Caudle says. "It's as if the teenage brain might need to work a little harder to hold that response back." This could help explain why teenage criminals are less likely to be repeat offenders, the researchers say—as their brains develop into adulthood, it gets easier for them to rein in their behavior.

"This work strongly suggests that the teenage brain is highly impulsive in the face of threat and points to unusual vmPFC activity as a possible biological underpinning," says Jon Horvitz, a neurobiologist at the City College of New York. "It is an exciting finding."