Karl Deisseroth, Peter Hegemann and Georg Nagel won the 2026 Nobel prize in physiology or medicine for research that allows scientists to control brain cells with light. Their work grew from a question about how a single-celled alga senses light—a line of inquiry with no obvious practical value or clear route to riches, the article says.
From Algae to Nerve Cells
Hegemann, at Humboldt University of Berlin, and Nagel, at the University of Würzburg, studied how Chlamydomonas detects light. Light-responsive proteins appear across the living world. Single-cell organisms use them to move toward or away from light, generate energy and respond to the demands of a 24-hour day.
The researchers found that Chlamydomonas uses a protein called channelrhodopsin. It sits in the cell’s outer membrane, with parts facing the surrounding water and the inside of the cell. The protein contains retinaldehyde, a small molecule that absorbs light.
When light strikes retinaldehyde, the molecule changes shape. Channelrhodopsin shifts shape too, opening a passage through the membrane. Positively charged particles, including sodium, then flow from the water into the alga. That sends a signal inside the cell and helps it swim.
Nerve cells also use charged particles, called ions, moving 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 could be placed in nerve cells and used to switch them on with light. Hegemann, Nagel and Deisseroth, a psychiatrist and bioengineer at Stanford University in California, went on to do just that.
Controlling Cells With Light
The resulting technique, optogenetics, lets scientists switch specific groups of nerve cells on and off, then observe what happens. Researchers deliver the channelrhodopsin gene to the cells they want to study, usually with a virus altered so it can't cause disease. The cells then produce the protein and respond to light.
In animals such as mice, scientists can send light into the brain through a thin optical fibre. When light reaches cells carrying channelrhodopsin, the protein opens and activates 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.
Scientists can use the method to test whether particular nerve cells play a part in memory, sleep, sensation or movement. In a 2012 experiment, a Massachusetts Institute of Technology team gave mice a mild electric shock in a particular cage and used optogenetics to tag nerve cells in the brain’s memory centre that were active during the fear-conditioning experiment.
Days later, the team activated those cells with light in a different cage. The mice froze in fear, as if they remembered the shock. Mice that hadn't been shocked did not freeze. The result showed that light had reactivated a specific memory. Deisseroth was one of the study’s authors.
Uses and Limits
Optogenetics has changed how scientists investigate the brain and nervous system, and researchers are studying possible therapeutic uses. The technique is in early-stage clinical trials for people with retinal degeneration.
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 can then respond to light and restore some vision. Researchers are also studying whether optogenetics could eventually help treat Parkinson’s and epilepsy.
The Nobel recognized research that began with a question about how Chlamydomonas swims toward light. The article says the question didn't address an urgent human-health need or offer a clear route to riches. It describes the eventual uses of knowledge as unpredictable. The article provides no figures on profits or commercial returns from optogenetics.