How the brain governs feelings, behaviours and bodily functions has long been a mystery. This year’s medicine laureates, Karl Deisseroth, Peter Hegemann and Georg Nagel, pioneered the field of optogenetics, which makes it possible to switch on, or off, the activity of individual nerve cells in a living brain. Using optogenetics, researchers have been able to reveal neural circuits governing specific memories, feelings and behaviours relevant for neurological and psychiatric disorders. In clinical medicine, researchers are using the method in attempts to restore sight in people with visual impairment. Listen to Peter Hegemann describe his feelings shortly after receiving the news about the prize: nobelprize.org/prizes/medici…