Until very recently scientists believed our brains were fully developed in childhood. Now thanks to imaging technology we know that the brain goes on developing and changing right through adolescence into adulthood. So what makes the adolescent brain different? Why does an easy child become a challenging teenager? And why is it that many mental illnesses begin during these formative years. Drawing upon her cutting-edge research award-winning neuroscientist Sarah-Jayne Blakemore explains how adolescence is fundamental to how we invent ourselves.