Three scientists win the Nobel Prize in Physiology or Medicine for a neuronal ‘light-switch’

Karl Deisseroth, Peter Hegemann and Georg Nagel have been awarded the 2026 Nobel Prize in Physiology or Medicine for discovering a way to activate and deactivate specific neurons in the brain using light. 

“Neuroscientists dreamed of a neuronal switch, a tool to turn specific neurons on or off with great precision,” said Abdel El Manira, a member of the Nobel Prize Committee, after describing this year’s Nobel Prize discoveries. This year’s laureates found a way to create this tool. 

This technology is known as optogenetics, and it is now used by researchers across the world. 

Through turning specific neurons on and off, neuroscientists can link neuronal circuits to specific behaviors. “We can get a functional map of the brain, exactly pinpoint which cells do what, which cells are responsible for creating behaviors or even emotions and memories in the brain,” said Anna Wedell, a member of the Nobel Prize committee, in an interview after the award was announced.  

This discovery began when Hegemann, a professor of neuroscience and biophysics at Umboldt University of Berlin, was studying single-cell algae in the early 1990s. He noticed the algae would move towards a light source. Driven by a curiosity to understand what motivated this single-celled organism, Hegemann discovered a gene for a light-sensitive protein in this algae. 

Hegemann collaborated with Negel, a biophysicist who had experience studying ion channels, and is currently a professor of Molecular Plant-Physiology at the University of Würzburg. They wanted to better understand the mechanism of this protein. Negel and Hegemann discovered that the protein was a channel. When light hit the protein, it opened, allowing ions to flow in creating an electrical signal. This was the first step in understanding what light could tell scientists about neurons and behavior, according to a science background by the Nobel Committee. Hegemann and Negel published their results in 2003 and named this protein channelrhodopsin-2. 

Negel tested this protein in several other cells than just the algae, including frog eggs, hamster kidney cells and embryonic human kidney. In all these cases, when the protein was added, the cells became sensitive to light. 

When Deisseroth, a psychiatrist and bioengineering professor at Stanford, heard of this discovery, he decided to test if this light-sensitive protein could work in a neuron. Deisseroth introduced the protein to neurons in rats. When he illuminated the cells, he noticed the cells “turned on,” causing certain behaviors in the mice. For the first time, neuroscientists were able to directly see a link between a neuron being activated and the corresponding behavior. 

Since the start of optogenetics, researchers have now used this tool to identify behaviors like parental care, aggression, anxiety, fear, even hunger and thirst in mice, according to a press release from the Nobel Committee. 

Beyond understanding the behaviors of the healthy brain, optogenetics have the potential to identify and possibly treat certain diseases in the brain,  El Manira said. Researchers have used optogenetics mouse models with diseases like dementia, epilepsy and addiction to understand which cells are active in these diseases, and possibly switch them on and off, said Wedell. 

While optogenetic research remains mostly confined to animal models, it has been used once in a human case as a partial vision restoration therapy. Scientists introduced the light-sensitive proteins into the remaining nerve cells of patients who had lost vision due to reduced eye photoreceptors function. Wedell said that this research remains in its early days, but the implications are fascinating.

“The brain is so complex, and we really have so little knowledge, and we desperately need this knowledge — to understand the healthy brain, but also all the diseases that it gets,” said Wedell. “Now we have something completely new to start to understand completely new things about the brain.”