Deisseroth, Hegemann and Nagel share the medicine Nobel for a light switch in nerve cells

The Nobel Assembly at Karolinska Institutet awarded the 2026 Nobel Prize in Physiology or Medicine on Monday to Karl Deisseroth, Peter Hegemann and Georg Nagel for discoveries that let researchers turn single nerve cells on and off with blue light. The citation is exact: discoveries concerning light-gated ion channels and optogenetics. The prize is 12 million Swedish kronor, shared equally. Physics, chemistry, literature, peace and the economics prize follow through the week, with the peace prize due on Friday.

Deisseroth, 54, holds the D.H. Chen professorship in bioengineering and in psychiatry and behavioural sciences at Stanford University and the Howard Hughes Medical Institute. Hegemann, 71, is Hertie senior professor of neuroscience at Humboldt University of Berlin. Nagel, 73, is professor of molecular plant physiology at the University of Würzburg. Reuters put their ages at those figures on the day of the announcement. The Assembly's own biographies give the birth years: Deisseroth 1971, Hegemann 1954, Nagel 1953.

An algal protein, then a switch

The work starts with a pond organism, not a clinic. Hegemann wanted to know how the single-celled alga Chlamydomonas swims toward light. In the early 2000s he and Nagel identified channelrhodopsin, a protein on the cell surface. Blue light opens a channel in the protein. Charged ions flow in. The cell fires an electrical impulse. The same protein made other cells light-sensitive once it was put into them.

Nagel tested the idea by injecting Chlamydomonas genes into frog eggs and found 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 produce electrical impulses under light. The Nobel summary places those discoveries at the Max Planck Institute for Biochemistry in Martinsried for Hegemann and at the Max Planck Institute for Biophysics in Frankfurt for Nagel.

Deisseroth took the gene into nerve cells from rats. Blue light triggered a nerve signal. He published that result in 2005. Two years later the same switch worked inside the brains of living mice. Thomas Perlmann, secretary-general of the Nobel Assembly, said the method makes it possible to switch the activity of individual nerve cells in a living brain on or off. Per Svenningsson, chair of the Nobel Committee for Physiology or Medicine, said optogenetics provides a way of mapping the brain that researchers could once only imagine.

What the older methods could not show

Twentieth-century brain maps mostly said which region sat next to which function. Stimulation, lesions and scans could associate an area with a task. They could not prove that one identified cell type caused a memory, a feeling or a movement. Optogenetics changes the experiment. A researcher can express the algal channel in one genetically defined set of neurons, deliver light through a fibre, and watch the animal's behaviour change while neighbouring cells stay dark.

Laboratories have used that control to pick out circuits tied to particular memories, feelings and behaviours that matter in neurological and psychiatric disease. The clinical line that has moved furthest is vision. Clinicians can put DNA for a light-sensing protein into remaining retinal neurons so those cells send signals when light hits them, bypassing cells that have died. The Nobel text describes this as an attempt to restore sight, not a finished treatment.

The people and the money

Deisseroth took a PhD at Stanford in 1998 and an MD there in 2000. Hegemann took his PhD in 1984 at the Max Planck Institute for Biochemistry in Martinsried. Nagel took his in 1988 at the University of Frankfurt. The prize money, 12 million kronor, is about 1.2 million dollars at the rate Reuters used on Monday. Each laureate's share is 4 million kronor if the split stays equal, which the Assembly said it would.

The medicine prize has been given since 1901. This year's award is unusual in joining a plant physiologist, a biophysicist and a psychiatrist-engineer on one citation. The protein came from an alga that hunts light. The use is a method for asking which nerve cell does what, in a living brain, on a timescale of milliseconds.

The open question is how far the clinical attempts go. Sight trials are the clearest medical use named by the Assembly. Psychiatric and neurological applications remain mostly laboratory maps. The prize does not claim a drug, a device on the market, or a change in how hospitals treat patients this week. It records that a channel from a green alga is now the standard way to prove that a given nerve cell causes a given act.