It starts with an alga, one that swims towards the light.
Peter Hegemann wondered how the single-celled Chlamydomonas does it. In the early 2000s he and Georg Nagel discovered a protein with unique properties on the surface of the cell: channelrhodopsin.
Fact
The facts: on 5 October 2026 the Nobel Assembly at Karolinska Institutet awarded the 2026 Nobel Prize in Physiology or Medicine to Karl Deisseroth (Howard Hughes Medical Institute and Stanford University, USA), Peter Hegemann (Humboldt University of Berlin, Germany) and Georg Nagel (University of Würzburg, Germany) “for their discoveries concerning light-gated ion channels and optogenetics”. Hegemann and Nagel discovered channelrhodopsin in the early 2000s, a protein on the surface of the single-celled alga Chlamydomonas. When it is illuminated with blue light, a channel opens through the protein, charged ions flow into the cell and it produces an electrical impulse; the two found that any cell they put the protein into becomes light sensitive. Deisseroth introduced the channelrhodopsin gene into rat nerve cells and triggered a nerve signal with blue light; he published it in 2005. Two years later he made this light-controlled switch work in the brains of living mice. The discoveries behind the prize were made at the Max Planck Institute for Biochemistry in Martinsried (Hegemann) and at the Max Planck Institute for Biophysics in Frankfurt (Nagel). The prize is 12 million Swedish kronor, shared equally between the three.
The prize is for an instrument. The old methods showed which areas of the brain affect which functions, but could not prove cause. The picture of the brain was a sketch map full of question marks, the Nobel Assembly writes. With the light switch you turn on chosen nerve cells and watch what changes.
Before the switch, the brain was a sketch with question marks.
The division of labour is clean. The first two find the protein in an alga, the third puts it into nerve cells and switches them on with light.
The Nobel Assembly lists what came out of it: with optogenetics, researchers have revealed circuits behind particular memories, feelings and behaviours relevant to neurological and psychiatric disorders. The chair of the Nobel Committee, Per Svenningsson, puts it this way: optogenetics makes it possible to map the brain in a way they could once only dream of.
The clinic is the other level, and the press release is restrained: researchers are using the method in attempts to restore sight in people with visual impairment. Attempts, not a cure.
Official primary sources
Nobel Assembly at Karolinska Institutet - Press release: Nobel Prize in Physiology or Medicine 2026, 05.10.2026The visual is generated code-art, no third-party images.