A Nobel for the light switch that tames brain cells — and a path toward restoring sight

Twenty years ago, Karl Deisseroth did something that sounded like science fiction: he shone blue light into the brain of a living mouse and switched individual nerve cells on and off. The trick relied on a light-sensing protein that Peter Hegemann and Georg Nagel had found in a humble pond alga. Today that technique — optogenetics — is used in labs worldwide to map the brain circuits behind memory, emotion, and behavior. And it's already in clinical trials aimed at restoring vision in people losing their sight. This week, Stockholm gave the trio medicine's highest honor for it.