Why do teenagers behave like — teenagers? We get an explanation from neuroscientist Dr. Frances Jensen, who says our brains are still maturing through our 20s and that the front part of the brain is the last to develop. "And what's in the front? Your frontal cortex and prefrontal cortex; these are the areas where we have insight, empathy, impulse control," she says. "Risk-taking behavior is suppressed by activity in your frontal lobes." Her book is 'The Teenage Brain.' Film critic David Edelstein reviews 'The Jungle Book.'