Now optogenetics will evolve into a revolutionary technique that allows scientists to switch individual nerve cells on and off with light
SRINAGAR: Karl Deisseroth, Peter Hegemann and Georg Nagel have been awarded the 2026 Nobel Prize in Physiology or Medicine for discoveries concerning light-gated ion channels and optogenetics, the Nobel Prize organisation said.
Their work has given scientists something earlier generations could only dream of: a way to switch individual nerve cells on or off with light and observe what happens inside a living brain.
The breakthrough has transformed neuroscience because the brain contains an extraordinarily complicated network of nerve cells. Scientists can now investigate which individual cells or groups of cells control particular functions, including movement, memory, pain, reward, attention and social behaviour.
Brain Mystery
The human brain weighs only about 1.3 kilograms, yet it stores memories, enables creativity and emotions, and controls basic functions such as breathing, heartbeat and sleep.
Scientists have studied the brain for centuries. In the 20th century, they identified areas associated with different functions, but the techniques available were relatively crude.
The resulting picture was, as the Nobel material puts it, rather like a blurry photograph. Scientists could identify broad regions of the brain but often could not prove that a particular type of nerve cell directly caused a particular behaviour or feeling.
Light Switch
One scientist who imagined a more precise approach was Francis Crick, who shared the 1962 Nobel Prize for the discovery of DNA’s double-helix structure.
Decades later, Crick became interested in consciousness and wondered whether individual nerve cells could somehow be switched on with light.
Nerve cells communicate extremely rapidly, so Crick reasoned that light might be an ideal control mechanism, if scientists could somehow make nerve cells respond to it. At the time, the idea appeared extremely difficult, perhaps even unrealistic.
The 2026 Nobel laureates eventually turned that idea into reality.
Algal Clue
The story began with a tiny green alga called Chlamydomonas.
In the early 1990s, Peter Hegemann wanted to understand how this single-celled organism could react so quickly to light.
Chlamydomonas swims towards light. It senses light using a tiny structure called an eyespot containing a light-sensitive molecule.
Hegemann measured the electrical signals produced when light reached the eyespot and discovered something remarkable: an electrical impulse appeared only about half a millisecond after illumination. That was astonishingly fast.
The human eye takes at least about 10 milliseconds to convert light into an electrical signal through a complex chain of chemical reactions. Hegemann wondered whether the alga possessed a much simpler mechanism.
Protein Hunt
Hegemann proposed that perhaps a single protein could both detect light and act as an ion channel, a gateway through the cell membrane through which charged particles could pass.
But finding the responsible protein proved difficult. The proteins became unstable when removed from the algal cells.
A breakthrough came around the turn of the millennium when Japanese researchers made the DNA sequence of Chlamydomonas available. Hegemann’s team found two genes resembling genes for known light-sensitive proteins. He then contacted Georg Nagel, who had the expertise needed to test the genes.
Channel Discovery
Nagel inserted the two genes separately into frog eggs.
The eggs began producing the corresponding proteins on their cell membranes. When Nagel illuminated the proteins, they opened like channels, allowing ions to flow through and creating an electrical signal.
The proteins were named channelrhodopsin-1 and channelrhodopsin-2.
The second protein proved especially important because it could later be used to make nerve cells responsive to light.
Channelrhodopsin-2 was extraordinarily fast. A channel opened within about 0.2 milliseconds after exposure to light.
Hegemann and Nagel then demonstrated that the protein could make mammalian cells light-sensitive. In 2003, they published their findings and proposed that channelrhodopsin-2 could be used to generate electrical impulses in cells using light.
Brain Connection
The next major step was taken by Karl Deisseroth. While studying medicine in the 1990s, Deisseroth spent time in a psychiatric clinic. He was struck by the suffering of patients and became interested in why disorders such as depression, autism and schizophrenia affect people in such different ways.
He realised that studying isolated brain cells or thin slices of brain tissue was not enough. To understand these conditions properly, scientists needed to know how nerve cells worked inside a living brain.
Deisseroth obtained the DNA encoding channelrhodopsin-2 from Nagel and introduced it into rat nerve cells grown in the laboratory. The experiment worked.
When blue light was directed at the modified nerve cells, they immediately produced nerve signals that could be transmitted to other cells. Deisseroth’s group published the discovery in 2005.
Living Brains
The real test was whether the technique could work inside a living animal.
Researchers soon discovered additional proteins that could switch nerve cells on or off using different wavelengths of light. In 2006, the new technique received the name optogenetics.
In 2007, Deisseroth’s group successfully activated specific nerve cells in the brains of living mice.
They inserted the gene for channelrhodopsin-2 into a particular type of nerve cell in the motor cortex, the part of the brain involved in movement. A thin optical fibre was then used to deliver light to the cells.
When the cells were illuminated, the researchers could control the movement of the mice’s whiskers.
The same year, researchers used optogenetics to activate cells believed to control wakefulness. When the cells were illuminated, sleeping mice woke up, confirming the scientists’ hypothesis.
Memory Control
One of the most striking demonstrations came in 2012, when Deisseroth worked with Susumu Tonegawa to investigate memory.
Researchers identified a group of nerve cells in mice that appeared to store a particular fear memory. Later, when they activated those same cells, the mice displayed signs of fear even though there was no immediate danger.
It was the first experiment demonstrating exactly which nerve cells were necessary for a particular memory.
The experiment showed why optogenetics was so powerful: instead of merely observing activity in the brain, scientists could manipulate selected cells and see what happened.
Brain Mapping
The human brain contains around 90 billion nerve cells, each forming thousands of connections with other cells.
These cells are densely interwoven. Nerve cells controlling completely different functions may sit next to one another, while a single nerve cell may extend its connections to a distant part of the brain.
Optogenetics allows researchers to identify which cells within these complicated networks perform particular jobs.
Researchers have used the technique to investigate neural circuits involved in pain, social behaviour, thirst, eating, reward and attention. They have also identified cells involved in the body’s daily biological clock and in fever responses.
Studies of behaviour have shown that even apparently simple activities can involve several separate neural circuits. In mice, for example, different circuits control different aspects of caring for young animals.
Beyond Brain
Optogenetics is not limited to the brain. Research has shown that the technique can be used to study how the nervous system interacts with other parts of the body.
Deisseroth has demonstrated that activity in the heart can influence emotions, with increased heart activity capable of reinforcing feelings of anxiety. Other researchers have identified specific cells in the gut that may help explain why some people prefer sugar to artificial sweeteners.
Medical Hope
The ultimate importance of the technology may lie in medicine.
The Nobel Prize organisation says optogenetics has provided new insights into psychiatric and neurological disorders including depression, anxiety, schizophrenia, Alzheimer’s disease and Parkinson’s disease.
Researchers have also begun testing whether the technique can itself become a treatment.
In ongoing clinical trials, scientists are attempting to restore vision in people who have lost sight because of retinitis pigmentosa, a disease that destroys the light-sensitive cells of the retina.
In one early step described by the Nobel organisation, a channelrhodopsin-like protein was introduced into the retina of a blind person. With the help of special glasses that delivered light, the person was able to recover enough vision to distinguish and grasp objects on a table.
Scientists are also exploring whether optogenetics could improve cochlear implants. Existing implants stimulate the auditory nerve electrically; light-based stimulation could potentially activate it more precisely.
Transformative Tool
The Nobel Prize organisation says the discoveries of Deisseroth, Hegemann and Nagel have produced an extraordinarily powerful tool that has transformed neuroscience.
What began with a simple question about how a microscopic alga senses light has ultimately given researchers a way to control individual nerve cells in living brains.
That ability is helping scientists move from simply observing the brain to testing, with remarkable precision, which cells cause particular memories, movements, emotions and behaviours.
The 2026 Nobel Prize in Physiology or Medicine therefore recognises not just the discovery of a light-sensitive protein, but the creation of a new way to explore one of humanity’s greatest remaining mysteries: how the brain works.
