Karl Deisseroth, Peter Hegemann and Georg Nagel won the 2026 Nobel prize in physiology or medicine for work that lets scientists switch brain cells on and off with light. The award recognizes their research into “light-gated ion channels and optogenetics,” a technique that gives researchers precise control over selected groups of nerve cells.
Their work began with a single-celled alga, Chlamydomonas, and a basic question: how does it sense light? Hegemann, at Humboldt University of Berlin, and Nagel, at the University of Würzburg, studied how the organism responds. Their research led from the movement of a microscopic cell to experiments that manipulate activity inside the brain.
From algae to nerve cells
Hegemann and Nagel discovered that Chlamydomonas senses light using a protein called channelrhodopsin. The protein sits in the alga’s outer membrane and contains a light-absorbing molecule called retinaldehyde. When light strikes the molecule, it changes shape. Channelrhodopsin then opens a passage through the membrane, allowing positively charged particles, including sodium, to flow into the cell. That movement sends a signal and helps the alga swim.
Nerve cells also rely on charged particles, or ions, crossing their membranes to control their activity. A flow of positively charged particles into a nerve cell can make it more active. The researchers realized they might use channelrhodopsin to switch nerve cells on by shining light on them. Hegemann, Nagel and Deisseroth, a psychiatrist and bioengineer at Stanford University in California, went on to do just that.
Optogenetics works by delivering the channelrhodopsin gene to the nerve cells scientists want to study, usually with a virus altered so it can’t cause disease. Those cells produce the protein and respond to light. In animals such as mice, researchers send light into the brain through a thin optical fibre. Cells carrying the protein respond; nearby nerve cells without it don’t.
Control in the laboratory
Researchers can target a small area and switch light on and off extremely quickly. To test whether a group of nerve cells is involved in memory, sleep, sensation or movement, they can activate those cells and observe what happens. The technique lets researchers manipulate selected neural activity and watch the consequences.
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, they activated those cells with light. The mice froze as if they remembered the shock. Mice that hadn’t been shocked didn’t freeze. The result showed that light had reactivated a specific memory. Deisseroth was one of the study’s authors.
From investigation to possible treatment
Optogenetics has changed scientists’ ability to investigate the brain and nervous system, and researchers are also studying possible therapeutic uses. The technique is in early-stage clinical trials for people with retinal degeneration. Researchers 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 may restore some vision.
Researchers are also studying whether optogenetics could eventually help treat Parkinson’s and epilepsy. Those uses remain under study; they’re potential future applications, not established treatments.
The Nobel recognizes work that began with asking how Chlamydomonas swims toward light. The question had no obvious practical importance, the article says: it didn’t address an urgent human-health need or offer a clear route to riches. Researchers couldn’t predict the work’s later uses when they first asked the question. A tiny organism’s response to light became a tool for controlling and observing specific brain cells.