Your teenage daughter gets top marks in school, captains the debate team, and volunteers at a shelter for homeless people. But while driving the family car, her text-messages her best friend and rear-ends another vehicle. How can teens be so clever, accomplished, and responsible and reckless at the same time? Easily, according to two physicians at Children's Hospital Boston and Harvard Medical School( HMS) who have been exploring the unique structure and chemistry of the adolescent brain. The teenage brain is not just an adult brain with fewer miles on it, says Frances E. Jensen, a professor of neurology. It's a paradoxical time of development. These are people with very sharp brains, but they're not quite sure what to do with them. In animals, the movement is coordinated by a cluster of neurons in the spinal cord called the central pattern generator( CPG). This produces signals that drive muscles to contract rhythmically in a way that produces running or walking, depending on the pattern of pulses. A simple signal from the brain instructs the CPG to switch between different modes, such as going from a standstill to walking.