Why many teenagers seek thrills, break rules and seem nonchalant about their own safety has been a question brain scientists have worked to answer in the last two decades. Laurence Steinberg, a professor of psychology at Temple, used functional magnetic resonance imaging to study the brains of teens. He found that teens are more sensitive than adults to rewards of situations or activities, and less sensitive to risks. There's an evolutionary explanation for this kind of behavior. In most mammals, adolescence is the time when individuals leave the family environment, Steinberg said.