The next revolution in medicine just might come from a new lab technique that makes neurons sensitive to light. The technique, called optogenetics, is one of the biggest breakthroughs in neuroscience in decades. It has the potential to cure blindness, treat Parkinson’s disease, and relieve chronic pain. Moreover, it’s become widely used to probe the workings of animals’ brains in the lab, leading to breakthroughs in scientists’ understanding of things like sleep, addiction, and sensation.