Karl Deisseroth, Peter Hegemann and Georg Nagel have won the 2026 Nobel Prize in Physiology or Medicine for discoveries that made it possible to switch individual nerve cells on or off with light. The award recognizes light-gated ion channels and optogenetics, a technique that combines genetic engineering with precisely delivered light to test how brain circuits cause behavior and disease.
Hegemann and Nagel’s work began with Chlamydomonas, a single-celled alga that swims toward light. They identified channelrhodopsin, a light-sensitive protein in the organism’s cell membrane. When light changes the shape of a molecule inside the protein, the channel opens and charged ions flow across the membrane, producing an electrical signal that helps the alga move.
That mechanism also fits the basic way nerve cells operate: charged particles crossing their membranes can increase or suppress cellular activity. Deisseroth and collaborators adapted microbial light-sensitive proteins for mammalian neurons. In a 2005 study, their team showed that engineered rodent nerve cells could be activated with blue light and that another light-sensitive protein could inhibit activity with yellow light. Flexible optical fibers allowed researchers to deliver light to selected cells and circuits in living animals.
Optogenetics gave neuroscientists a way to isolate specific populations of cells and test cause and effect with high spatial and temporal precision. In a 2012 mouse experiment, researchers tagged neurons active during fear conditioning and later reactivated those cells in a different setting; the animals froze, while mice that had not undergone the conditioning did not. The finding showed that stimulating a defined neural population could reproduce a memory-related response.
The method has also been used to investigate circuits involved in movement, sleep, sensation, social behavior, depression and Parkinson’s disease. Early-stage clinical trials are testing optogenetic approaches for retinal degeneration by making surviving retinal cells responsive to light after rods and cones have been lost. Those investigations remain distinct from the Nobel-recognized research tool itself and do not establish a general treatment for neurological disease.