Studies have linked risky behavior in teens to a variety of factors, including chemical imbalances, peer pressure, trauma, exposure to lead, too much protein and not enough carbohydrates, rejection by peers and television. Risky behavior has also long been identified with race and ethnicity and family income and structure. But in the fall 1998 issue of the Journal of American Psychology, neuropsychologist Deborah Yurgelun-Todd, Director of Neuropsychology and Cognitive Neuroimaging at McLean Hospital Brain Imaging Center, the psychiatric teaching hospital at Harvard University, linked risky behavior in teens to their underdeveloped prefrontal cortexes.

Using functional magnetic resonance imaging (MRI) to compare the emotional processing of healthy 10- to 18-year-olds with that of normal adults, researchers focused on the level of brain activity in the amygdala, a region that guides instinctual or