[2026 Nobel Prize] Turning Brain Cells On and Off with Light... Three Pioneers of 'Optogenetics' Win Nobel Prize in Physiology or Medicine (Comprehensive)

Deisseroth, Hegemann, and Nagel Share the Prize... 'Light Switch' Discovered in Green Algae
Precise Control of Neurons at the Millisecond Level
"A Paradigm Shift in Neuroscience"

By simply shining light, it is possible to turn specific neurons in a living brain on and off. This allows scientists to directly confirm which neurons are responsible for forming memories, triggering emotions, or causing movement. Optogenetics—which began with foundational research exploring how single-celled green algae move toward light—has become the focus of this year’s Nobel Prize in Physiology or Medicine.

On October 5, 2026 (local time), the Nobel Assembly at the Karolinska Institute in Sweden announced that Karl Deisseroth, Professor at Stanford University in the United States; Peter Hegemann, Professor at Humboldt University in Berlin, Germany; and Georg Nagel, Professor at the University of Würzburg, Germany, have been jointly awarded the 2026 Nobel Prize in Physiology or Medicine. Their award was given for their discoveries related to light-gated ion channels and optogenetics.

Photo by Niklas Elmehed/Nobel Prize Outreach. Selected as the 2026 Nobel Prize laureates in Physiology or Medicine are Karl Deisseroth (from left), Peter Hegemann, and Georg Nagel. They jointly received the award for their discoveries related to light-gated ion channels and optogenetics.

Optogenetics is a technology that controls the activity of specific neurons using light. After inserting proteins that respond to light into neurons, exposing them to light at a particular wavelength allows scientists to selectively turn specific neurons on or off. Unlike conventional electrical stimulation, which also stimulates surrounding cells, optogenetics can specifically target a particular type of neuron and control its activity with millisecond (one thousandth of a second) precision.

'Light Switch' Discovered in Green Algae

The starting point for optogenetics was not the human brain, but the single-celled green alga called Chlamydomonas, which swims in water. This microorganism detects light and moves in the direction of illumination. Hegemann and Nagel studied the 'channelrhodopsin' involved in this process and discovered that when exposed to light, a channel opens up, allowing ions to enter the cell.

A single-celled green alga Chlamydomonas moving toward light. During the study of Chlamydomonas' light-sensing mechanism, channelrhodopsin, an ion channel that responds to light, was discovered. This discovery later became the foundation of optogenetics. Provided by the Nobel Prize Committee in Physiology or Medicine

In 2005, Deisseroth’s research team succeeded in inserting the channelrhodopsin-2 (ChR2) gene into mammalian neurons and triggered neural activity with blue light at the millisecond level. The light-detecting mechanism found in algae had thus been transformed into a 'light switch' for brain cells.

Wondo Heo, Professor of Biological Sciences at KAIST and a world-renowned expert in optogenetics, explained the difference from electrical stimulation. “With electrical stimulation, many surrounding neurons are activated simultaneously,” he noted. “A major advantage of optogenetics is that you can activate only desired neurons with millisecond precision.” The degree of neuronal activation can also be controlled by adjusting factors like light intensity and duration of stimulation.

Illustration depicting the principle of optogenetics. After expressing light-responsive proteins in specific neurons and then shining light, the activity of the neurons can be precisely controlled. This has made it possible to clarify the causal relationship between specific neural circuits and behavior, emotions, and cognition. Provided by the Nobel Assembly at the Karolinska Institute

Thanks to this technology, scientists are now able not only to observe the brain, but also to directly manipulate specific neurons to see how behaviors change as a result. Daesoo Kim, Professor of Brain and Cognitive Sciences at KAIST, stated, “This opens up a path to dissect neural circuits and study their functions according to cell type.”

The discoveries of the three laureates are interconnected: Hegemann and Nagel identified the existence and function of channelrhodopsin in green algae, and Deisseroth developed this into a research tool for controlling mammalian neurons.

Potential Beyond Brain Research: Toward Disease Treatment

Optogenetics has become an essential tool for studying a wide range of brain functions, including memory, emotion, sleep, and movement.

Joonki Kim, Professor in the Department of Convergence Medicine at Asan Medical Center, explained, “By using optogenetics in experimental animals, we can not only understand the function of certain brain circuits at the cellular and molecular level, but also test hypotheses about the effects of new drugs being developed for the brain.” Optogenetics is also being employed to uncover the causes of neurological disorders such as Parkinson's disease, epilepsy, and sleep disorders, as well as to verify new therapeutic targets and drug candidates.

However, it is not yet at the stage where it can be directly used to treat brain diseases in humans. Professor Heo noted that this Nobel Prize is significant not because of clinical advances, but rather due to its profound impact in fundamental brain science research. Challenges remain, such as safely delivering light deep inside the brain and ensuring light-sensitive proteins are delivered only to the targeted neurons.

Principles of Animal Experiments Using Optogenetics. After expressing channelrhodopsin-2 (ChR2) in specific neurons of mice, illuminating the neurons with light through an optical fiber allows precise control of the neuronal activity. Courtesy of the Nobel Prize Committee in Physiology or Medicine

Attempts to apply this technology to humans have already begun, with vision restoration as a leading example. In this approach, light-sensitive proteins are expressed in the retinal cells of patients whose ability to sense light has been impaired, in an effort to restore light responsiveness.

Sang Yup Lee, Distinguished Professor of Chemical and Biomolecular Engineering at KAIST, commented, “The originality of this research lies in successfully turning the light-detecting protein channelrhodopsin from single-celled microalgae into a light switch for mammalian neurons. This is an excellent example of how basic research driven by curiosity can evolve into an innovative biomedical technology.”

Last year, Deisseroth visited Korea after being selected as the recipient of the 18th Asan Foundation Medical Award in Basic Medicine. This year, the Nobel Prize award amount increased to 12 million Swedish kronor (about 1.6 billion won), up 1 million kronor from last year’s 11 million. The three co-winners will share the prize money. This year’s Nobel Prize announcements will continue with Physics on the 6th, Chemistry on the 7th, Literature on the 8th, Peace on the 9th, and Economics on the 12th.

This content was produced with the assistance of AI translation services.