Why do teenagers seem so much more impulsive, so much less self-aware than grown-ups? Cognitive neuroscientist Sarah-Jayne Blakemore compares the prefrontal cortex in adolescents to that of adults, to show us how typically "teenage" behaviour is caused by the growing and developing brain.

Sarah-Jayne Blakemore is Professor of Psychology at the University of Cambridge, UK, and leader of the Developmental Cognitive Neuroscience Group.