The Nobel Prize in Physiology or Medicine for 2026 was jointly awarded to Karl Deisseroth, Peter Hegemann and Georg Nagel for their discovery of an algal protein that reacts to light and its use as a switch to study functions of nerve cells.
Their explorations led to creation of a new field of study called optogenetics, which may finally help scientists understand how brain forms memories, feelings and behaviours.
"We were able to precisely pace the heart and look at effects that different heart rates have on brain states... Communication across the body, from the body to the brain, but with precision of a gain of function in a peripheral organ allowing us to see effects on brain and behavioural state... this ability to execute a precision intervention in one organ and read out effects in complex behaviours - this is something that people have wanted for a long time to be able to do," said Deisseroth.
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In simple terms, they found a way to control cells with light. Imagine brain is a vast electrical network containing billions of tiny cells called neurons. These neurons communicate by sending electrical signals, allowing us to move, see, remember, feel pain and experience emotions. Deisseroth, Hegemann and Nagel helped scientists develop a remarkable way of controlling these electrical signals: using light.
Their research led to discovery and development of light-sensitive proteins, called opsins, that can be placed in specific cells. When light is directed at those cells, proteins act like tiny switches, turning cells' activity on or off. This is known as optogenetics - essentially, using light to control genetically modified cells.
What is optogenetics? It is a field of research that uses light to manipulate activity of neurons or other types of cells and study resulting effects. This is done by expressing light-sensitive protein in targeted cells. Within brain, it has contributed towards identifying neural circuits responsible for sensing pain, social behaviours, thirst, food consumption, reward and attention or understanding of how memories are created.
Interestingly, field rests on a theory proposed by Francis Crick, molecular biologist who was behind discovery of double helix structure of DNA, and was awarded Nobel prize for it. He envisioned activating individual nerve cells in brain to investigate mechanisms that underlie human consciousness. With nerve signals being extremely rapid, he realised it would only be possible if scientists were somehow able to manipulate nerve cells with light. He himself admitted that idea sounded far-fetched.
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But it was made possible by work of Hegemann and Nagel on alga Chlamydomonas. These are famous for their ability to quickly swim towards a light source. Hegemann found that these reacted extremely quickly, within half a millisecond after light reached a tiny orange dot - called eyespot - that alga used to detect light. For reference, it takes 10 milliseconds for human eye to react to light. Hegemann wondered, how could response to light be more than 20 times faster in Chlamydomonas?
He hypothesised that a single protein complex both captured light and acted on it in alga as opposed to multi-step process in human eye. Yet, finding this protein was a challenge because when proteins in algal eyespot were removed from their natural setting, they became unstable and easily damaged. This is when he discovered that Japanese researchers had mapped DNA of Chlamydomonas, among which were codes for two genes that shared similarities with light-capturing proteins.
Enter Nagel. He used egg cells of frogs to express two proteins and confirm Hegemann's hypothesis. Alga detected and reacted to light using protein channelrhodopsin-2 (ChR-2). They introduced channels in different types of cells and found that they all became light sensitive.
Deisseroth found that ChR-2 could control activity of specific nerve cells in manner proposed by Francis Crick. He used it to control rat nerve cells in a petri dish and later in rats. With Deisseroth's lab at forefront, researchers soon found more proteins that can turn nerve cells on and off, and which are activated by different wavelengths of light.
Why the field matters: 'Optogenetics has given us an extremely powerful way to switch on and off neurons and see what happens. It has allowed us to manipulate nerve cells and study its effects with an unprecedented level of precision. It has completely changed scale at which discoveries are happening in neurosciences,' said Vaidya, a senior professor at Tata Institute of Fundamental Research.
"Optogenetics is still largely used in laboratories to see what set of neurons regulates what type of behaviour in animals, helping scientists look into black box", Vaidya says. Dr Sanjeev Kumar Mahto, professor at IIT BHU, said it has allowed scientists to see functions of brain and enhance understanding of what causes certain conditions.
Deisseroth's research group introduced gene for ChR-2 in 2006 and successfully used light to activate neurons and control movements of mouse whiskers. Same year, he used technique to wake sleeping mice by manipulating a recently discovered type of nerve cell that was suspected to control wakefulness. His team also studied brains of mice as they experienced fear, and noted which nerve cells appeared to form memory. When they later reactivated these nerve cells, mice showed signs of fear, despite not being in danger at time.
What kind of therapies are being developed based on this field? There are ongoing clinical trials on restoring vision in people who have become blind due to retinitis pigmentosa, a disease that destroys eye's rods and cones. Using special glasses emitting light, person was able to discern and grasp objects on a table. There are also hopes that optogenetics could improve cochlear implants. Currently, these implants stimulate auditory nerve using electricity.
Tags: #NobelPrize2026 #Optogenetics #Neuroscience #KarlDeisseroth #PeterHegemann #GeorgNagel #TIFR