In this article, the author describes how researchers study the adolescent brain--a subject of inquiry that did not exist a generation ago. Any parent of a teenager knows that adolescents often have difficulty navigating through their world. Now scientists are starting to find out why. Peering into the minds of maturing youngsters, researchers are discovering what happens within the developing brain that can steer adolescents into risky territory. Along with several other researchers, Beatriz Luna, an associate professor of psychiatry and psychology at the University of Pittsburgh, has switched to studying the adolescent brain by classifying what is particular about adolescence that makes it vulnerable. Through new experimental techniques that illuminate the thoughts of youngsters and through research on animals, investigators have found that the brains of teenagers are changing far more than was previously thought. And the way their minds ripen seems specifically to lead them into danger.