Stir a single-celled green alga called Chlamydomonas into a dish of water, shine a light on one side, and the faint green tint drifts toward the glow. In the early 1990s a German biophysicist named Peter Hegemann wanted to know how something with no eyes and no brain manages that. On Monday his question, and what came of it, won a Nobel Prize.
The Nobel Assembly at Karolinska Institutet awarded the 2026 Prize in Physiology or Medicine to Hegemann, Georg Nagel and Karl Deisseroth “for their discoveries concerning light-gated ion channels and optogenetics.” Hegemann and Nagel found a protein in the alga that opens like a gate when light hits it. Deisseroth put that protein into nerve cells and turned it into a switch. Researchers can now turn chosen brain cells on and off with flashes of light and watch what an animal does. The three share 12 million Swedish kronor, about $1.2 million, Nature reported.
“Optogenetics provides opportunities for mapping the brain in a way that we could once only dream of,” Per Svenningsson, who chairs the Nobel Committee for Physiology or Medicine, said in the prize announcement.
Half a millisecond in an algal eyespot
The alga senses light through an eyespot, a tiny orange dot on its surface. When Hegemann measured it with fine electrodes at the Max Planck Institute for Biochemistry near Munich, he found an electrical response half a millisecond after light arrived, according to the committee’s popular-science background. That was startling. In the human eye, light sets off a chain of chemical steps before an ion channel opens and a nerve signal starts, and the whole sequence takes at least 10 milliseconds. The alga was more than 20 times faster.
Hegemann proposed that a single protein was doing both jobs, catching the light and acting as the channel. Colleagues were skeptical, the committee writes. No known ion channel could respond to light on its own, and the proteins in the eyespot fell apart when he tried to purify them.
The break came around 2000, when Japanese researchers published a large set of Chlamydomonas gene sequences. Hegemann’s group spotted two genes that resembled known light-catching proteins and sent them to Nagel at the Max Planck Institute for Biophysics in Frankfurt. Nagel’s method was to inject genes into frog eggs, which then produce the protein on their surface where it can be tested. Under light, the new proteins opened within fractions of a millisecond and let charged ions flow. Hegemann’s decade-old hypothesis was right.
The proteins were named channelrhodopsin-1 and channelrhodopsin-2. In 2003, with biophysicist Ernst Bamberg, Nagel and Hegemann reported that the second one made even human kidney cells light-sensitive, and suggested it could be used to trigger electrical signals in cells on demand.
From frog eggs to a mouse’s whiskers
Deisseroth, a Stanford psychiatrist and bioengineer, was looking for exactly that kind of tool. The committee writes that training at a psychiatric clinic, where treatments were rarely effective and often had debilitating side effects, pushed him to look for a way to study the living brain directly. He wrote to Nagel and asked for the gene.
In 2005 his lab reported that rat nerve cells carrying channelrhodopsin-2 fired on cue when hit with blue light, with millisecond timing. The technique got its name, optogenetics, in 2006. In 2007 the team put the gene into motor neurons of living mice, threaded a thin optical fiber through a small hole in the skull, and moved the animals’ whiskers with light, the committee’s background says.
That set off a wave of experiments. Researchers have used the method to wake sleeping mice, map circuits for pain, thirst, reward and attention, and show that separate circuits control different parts of a single behavior, such as how mice gather their pups and how they groom them. In 2012 Deisseroth and Nobel laureate Susumu Tonegawa reactivated the specific cells holding a mouse’s fear memory and saw the animal freeze with no threat present. The committee calls it the first experiment showing exactly which nerve cells a specific memory needs.
Deisseroth described the inversion behind it to STAT. In science and medicine, light has usually been a way to observe. Here, he said, “we’re using light to cause things to happen.”
An idea Crick floated, and names the prize leaves out
The idea is older than the tool. Francis Crick, who shared the 1962 Nobel for the structure of DNA, suggested in 1979 and again in 1999 that neuroscience needed a way to control specific cell types precisely, and that light might be the way to do it, the committee’s scientific background notes. Committee member Abdel El Manira told reporters it was “a brilliant idea, but it seemed entirely far-fetched,” Scientific American reported.
Others got partway there before 2005. The committee’s scientific background credits Austrian neuroscientist Gero Miesenböck with the first genetic method for making ordinary nerve cells respond to light, published in 2002. It used three proteins borrowed from the fruit fly’s visual system, and the committee describes it as too slow and not fully genetically encoded, because it needed added chemicals. The background also cites a 2006 paper from the lab of Zhuo-Hua Pan, a vision scientist at Wayne State University, that put channelrhodopsin-2 into the retina. According to STAT, Pan’s team had the experiment working in 2004 and submitted it by the end of that year. By the time the paper appeared in 2006, the Stanford results had already been published.
The other name raised Monday was Ed Boyden. He was the first author of the 2005 paper, written while he was a Ph.D. student in Deisseroth’s lab, with Feng Zhang, Bamberg, Nagel and Deisseroth as co-authors. STAT reported that many commentators on social media said Boyden, now at MIT, should not have been left out. Boyden didn’t respond to STAT, and the committee chair declined to explain the choice of winners. The Nobel rules allow at most three laureates per prize.
Where the light switch is heading
The method requires adding a gene to the target cells and getting light to them. The first human result came from the eye, where light reaches the cells on its own.
In 2021, a team led by José-Alain Sahel and Botond Roska reported in Nature Medicine on a man blinded by retinitis pigmentosa, a disease that destroys the eye’s light-sensing rods and cones. They injected one eye with an engineered virus carrying the gene for ChrimsonR, a light-sensitive protein related to channelrhodopsin, into retinal cells that survive the disease. He then wore goggles that turned the scene in front of him into pulses of light projected onto his retina. With the goggles on, he could find, count and touch objects on a table using the treated eye. He could do none of that before the injection, or without the goggles afterward. He did not regain color or fine detail, and it was a single patient. The committee says clinical trials of the approach are ongoing.
The committee also points to hearing. Today’s cochlear implants stimulate the auditory nerve with electricity. Light might activate the nerve more precisely. In the lab, the method has already been used to study depression, anxiety, schizophrenia, Alzheimer’s and Parkinson’s, and to show links between the brain and the heart and gut. Deisseroth has shown, for example, that forcing the heart to work harder can reinforce feelings of anxiety.
Deisseroth told Nature he was just drifting off to sleep after a late night of work when his bedside phone rang. He said he had trouble forming words for about 30 seconds.
The committee’s press release, popular-science background and scientific background are posted on nobelprize.org.
Medicine Nobel: How a Light-Chasing Alga Became a Switch for the Brain
Sources
- Nobel Assembly at Karolinska Institutet, press release (Oct. 5, 2026). Used for: the laureates and citation, Svenningsson’s quote, the 2005 and 2007 milestones, affiliations.
- Nobel Committee, “A light-sensitive algal protein energised neuroscience,” popular information (Oct. 5, 2026). Used for: the algae experiments and timings, the frog-egg tests, Deisseroth’s path, the mouse experiments, the fear-memory study, clinical and cochlear uses.
- Nobel Committee, scientific background (Oct. 5, 2026). Used for: Crick’s 1979 and 1999 proposals, Miesenböck’s 2002 work, Bamberg’s role, the 2006 retina paper from Pan’s lab.
- STAT, “2026 Nobel Prize in Medicine awarded for brain research tool called optogenetics” (Oct. 5, 2026). Used for: Deisseroth’s remarks, the Boyden discussion, Pan’s 2004 work and publication timeline, the committee chair declining to comment.
- Nature, “Medicine Nobel awarded for brain ‘switch’ that controls neurons with light” (Oct. 5, 2026). Used for: the prize amount in dollars, Deisseroth’s account of the call, the 2005 paper’s authors.
- Scientific American (Oct. 5, 2026). Used for: El Manira’s remarks on Crick’s idea.
- Sahel, Roska et al., “Partial recovery of visual function in a blind patient after optogenetic therapy,” Nature Medicine (2021) and STAT (May 24, 2021). Used for: the vision-restoration case.
- Howard Hughes Medical Institute, “Karl Deisseroth Awarded the 2026 Nobel Prize in Physiology or Medicine” (Oct. 5, 2026). Used for: Deisseroth’s role and affiliation.