Karl Deisseroth, Peter Hegemann and Georg Nagel won the 2026 Nobel prize in physiology or medicine for research into “light-gated ion channels and optogenetics,” a technique that lets scientists control brain cells with light. Their work began with a question: how does a single-celled alga detect light?
From Algal Cell to Light Signal
Hegemann, at Humboldt University of Berlin, and Nagel, at the University of Würzburg, studied how Chlamydomonas senses its surroundings. Light sensing occurs across the living world, not just in animals with eyes. Single-cell organisms use light-responsive proteins to move toward or away from light, generate energy and respond to environmental changes across a 24-hour day.
The researchers found that Chlamydomonas uses a protein called channelrhodopsin. It sits in the outer membrane of the algal cell, with part of the protein facing the surrounding water and part facing inward. Channelrhodopsin contains retinaldehyde, a small molecule that absorbs light.
When light hits retinaldehyde, the molecule changes shape. That shift opens a passage through the cell membrane. Positively charged particles, including sodium, then move from the water into the alga. The movement sends a signal inside the cell and helps it swim.
Nerve cells also use charged particles, called ions, that move across their membranes to control activity. A flow of positively charged particles into a nerve cell can make it more active. The researchers saw that channelrhodopsin might switch nerve cells on with light. Hegemann, Nagel and Deisseroth, a psychiatrist and bioengineer at Stanford University in California, went on to apply the technique.
How Optogenetics Tests Brain Activity
Scientists deliver the channelrhodopsin gene to the nerve cells they want to study, usually using a virus altered so it can't cause disease. Those cells then produce the protein and respond to light. In animals such as mice, researchers can send light into the brain through a thin optical fibre. Cells containing channelrhodopsin activate when the light reaches them; nearby nerve cells without the protein aren't affected.
Researchers can target a small area and switch the light on and off extremely quickly. They use that control to test whether specific groups of nerve cells play a role in memory, sleep, sensation or movement, then observe what happens when those cells are activated.
In a 2012 experiment, a Massachusetts Institute of Technology team gave mice a mild electric shock in a particular cage. The researchers used optogenetics to tag nerve cells in the brain's memory centre that were active during the fear-conditioning experiment. Days later, in a different cage, the team activated those cells with light. The mice froze in fear, as if they remembered the shock. Mice that hadn't been shocked didn't freeze. Deisseroth was one of the study's authors.
Research and Potential Treatment
Optogenetics has transformed scientists' ability to investigate the brain and nervous system. Researchers are also studying the technique for possible medical uses, though its use for people with retinal degeneration remains in early-stage clinical trials.
In that research, scientists introduce light-sensitive proteins into nerve cells that remain in the retina after rods and cones—the cells that normally detect light—have been lost. The surviving cells may then respond to light and restore some vision. Researchers are also studying whether optogenetics could eventually help treat Parkinson's and epilepsy.
The Nobel recognizes research that began with a question about how Chlamydomonas swims toward light. At the outset, the article says, that question had no obvious practical importance: it didn't address an urgent human-health need or offer a clear route to riches. The research's eventual applications, including its use to study memory and potential therapeutic uses, grew from investigating how the alga responds to light. Robert Lucas wrote the article; The Conversation first published it, and Daily Maverick republished it.