Karolinska awards the 2026 medicine prize for the light switch in nerve cells

The Nobel Assembly at Karolinska Institutet on Monday awarded the 2026 prize in physiology or medicine to Karl Deisseroth, Peter Hegemann and Georg Nagel for discoveries concerning light-gated ion channels and optogenetics. The three will share 12 million Swedish kronor, about 1.2 million dollars at recent rates.

Deisseroth, 54, works at the Howard Hughes Medical Institute and Stanford University. Hegemann, 71, is at Humboldt University of Berlin. Nagel, 73, is at the University of Würzburg. Thomas Perlmann, secretary-general of the assembly, said the method makes it possible to switch individual nerve cells in a living brain on or off.

An alga that opens under blue light

The useful protein came from a single-celled green alga, Chlamydomonas. Hegemann and Nagel found that a protein on the alga, later called channelrhodopsin, opens a channel when blue light hits it. Charged ions then flow across the membrane and the cell produces an electrical impulse. The protein does this regardless of the cell type it sits in. That is the practical point. Put the gene into a cell that does not normally respond to light, and light becomes a remote control.

Nagel tested the idea by injecting Chlamydomonas genes into frog eggs and identified channelrhodopsin-2, a light-sensitive ion channel. In 2003 he and Hegemann reported that the protein could be introduced into human and hamster cells and generate electrical impulses with light. Hegemann was born in 1954 and took his doctorate in 1984 at the Max Planck Institute for Biochemistry in Martinsried. Nagel was born in 1953 and took his doctorate in 1988 at the University of Frankfurt. The Nobel citation places his discovery work at the Max Planck Institute for Biophysics in Frankfurt.

From a dish of rat neurons to a mouse

Deisseroth took the protein into nerve cells. Born in 1971, he earned a PhD from Stanford in 1998 and a medical degree there in 2000. In 2005 he published the result that turned the alga protein into a laboratory tool: the channelrhodopsin gene, placed in rat nerve cells, let light trigger nerve signals. Two years later, in 2007, he made the same switch work in the living brain of a mouse.

That step is what the field now calls optogenetics. A researcher can label a chosen set of neurons with the light-sensitive channel, shine a thin fibre of light into the tissue, and watch what the animal does when those cells fire, or when they are silenced by a different channel. Memory circuits, fear circuits and movement circuits can be tested one class of cell at a time. Older methods could correlate a brain region with a behaviour. This method can ask whether those cells are enough to cause it.

Per Svenningsson, chair of the Nobel Committee for Physiology or Medicine, said optogenetics provides opportunities for mapping the brain in a way that researchers could once only dream of. The assembly's press release said the laureates had laid the foundation of a new era in neuroscience, because the tool shows how nerve cells shape memories, feelings and behaviours in the living brain.

What the clinic has and has not done with it

The prize is for a basic method, not for an approved drug. Researchers are using the same light-gated channels in attempts to restore sight in people with visual impairment. Science magazine reported on Monday that the method has been adapted so that a few blind people have regained modest sensitivity to light, and that it is also being tested in epilepsy and pain. Those trials are small. They do not yet amount to a standard treatment, and the Nobel citation does not claim they do.

The prize sum is the standard 12 million kronor, divided equally. Physics, chemistry, literature, peace and the economics prize follow through the week. The peace prize is due on Friday.

The concrete takeaway is mechanical. A protein from an alga that opens under blue light, moved into a nerve cell by Deisseroth in 2005 and into a living mouse brain in 2007, is now the switch laboratories use when they want to know which cells cause a behaviour. The clinical tests in vision, epilepsy and pain sit downstream of that switch, and they are still experiments.