Optogenetics is a technique that uses light to switch brain cells on and off. It won the 2026 Nobel Prize in Physiology or Medicine for Karl Deisseroth, Peter Hegemann and Georg Nagel.

The story starts with algae. Hegemann discovered a light-sensitive protein called channelrhodopsin in green algae. The protein opens a channel in the cell surface when struck by light, letting ions flow in.

Deisseroth realised the same trick could work in neurons. His team inserted the protein into specific groups of brain cells in living animals. Thin optical fibres then shine tiny beams of light deep into the brain. Blue light tells the cells to fire. Yellow light silences them.

The idea answered a challenge posed decades ago by Francis Crick, who co-discovered the structure of DNA. He said neuroscience needed a way to control one type of brain cell while leaving others untouched.

Today optogenetics is used by thousands of neuroscience groups worldwide. Researchers are applying it to Parkinson’s disease, epilepsy, anxiety and depression. A Stanford-linked company, Circuit Therapeutics, is exploring clinical trials to treat chronic pain.

The Nobel citation honours “discoveries concerning light-gated ion channels and optogenetics.