Karl Deisseroth, Peter Hegemann and Georg Nagel share the 2026 Nobel Prize in Physiology or Medicine, honouring their work on optogenetics and light-gated ion channels. Hegemann and Nagel found channelrhodopsin, a protein that lets cells react to light. Deisseroth then used the method to steer nerve cells with light, including inside the brains of living mice. Optogenetics lets researchers switch chosen nerve cells on or off with light, helping study brain functions like memory and movement. It is widely applied in research on Parkinson's disease, depression and addiction. Selection of the winners rests with the Nobel Assembly of Sweden's Karolinska Institute.