Long read: Stanford University professor Karl Deisseroth wins 2026 Nobel Prize in physiology or medicine

It is that time of the year when distinguished scientific work contributing to human progress gets recognised – the week when Nobel prize winners are announced. This article features one who shared this year’s award in the field of medicine – Karl Deisseroth of Stanford University for his work in the new and exciting field of Optogenetics. He shared the award with Peter Hegemann from the Humboldt University of Berlin and Georg Nagel from the University of Würzburg in Germany

Over the years, medical science has progressed significantly establishing cures for cancer and cardio-vascular diseases among others. However, cures for neurological illnesses related to the brain such as Alzheimer’s and Parkinson’s have still remained out of reach. Optogenetics hopes to provide this elusive breakthrough.

“Deisseroth established his preeminence as a leader in neuroscience by developing a process to insert light-sensitive microbial proteins called opsins into mammalian brain cells, allowing selected cells to be controlled by light.”

In his own words, “Optogenetics is an engine for discovery…It’s for probing complex systems at the fundamental level of cells. We want to understand how the brain works as an intact system to carry out complex cognitions, behaviors and perceptions while being anchored and grounded in the elemental cellular level. We are already taking steps to understand healthy brain function and understand how things go wrong. This is the key principle of optogenetics: precise causal perturbation. Then you can search for ways to perhaps correct the anomalies. Once you know the cells that are important in a symptom or in correcting a symptom, then you can design any method you like to target their activity.”

He first wrote in detail in this 2010 piece for the Scientific American for those interested. But here’s a simplified explanation from this Stanford Medicine article:

“Before the advent of optogenetics, there were two main experimental workhorses for studying the brain: electrical stimulation and drugs. Exciting neurons, or nerve cells, by stimulating them electrically elicits an immediate response — but also trips off responses in neighboring brain cells and circuits other than the one being studied. And while electrical stimulation can activate neurons, it can’t precisely inhibit them, which is critical to studying brain function.

Drugs, too, are imprecise. They can selectively activate or inhibit neurons — but not necessarily only those in the circuit of interest. Plus, they diffuse widely and can’t be mopped up quickly, making them poor on/off switches.

What if you could install traffic lights in the neurons threading through a living brain, so that you could start or stop traffic on them and observe the effect? The new technology mixes optics, genetic engineering and a mix of other disciplines. It literally uses light to control the messages zinging along our nerves. The go signal can be blue, while the stop signal may be yellow. Both are photosensitive proteins called opsins, originally discovered in microbes.

The team genetically engineered the opsin so it could be expressed on the surface of specified rodent nerve cells and would fire when zapped with blue light — a technique published in Nature Neuroscience in 2005 and now used regularly. They rendered the method more practical by designing a method of inserting an ultrathin, flexible optical fiber into live rodents’ brains so researchers could shoot light directly into specific nerve cells or circuits from a distance, allowing them to control the rodents’ behavior. The team also successfully devised an opsin, triggered by yellow light, that inhibited the activity of nerve cells.

Now, neuroscientists use many colors of light and can manipulate cell behavior without direct genetic engineering. Deisseroth has likened subsequent advances in the field to the addition of instruments to the “optogenetic orchestra.””

The use cases are already here: “Working with University of California, San Francisco, researcher Anatol Kreitzer, PhD, Deisseroth discovered two nerve-cell circuits that play a key role in Parkinson’s disease, a progressive disorder that affects the nervous system.

Using optogenetics, Deisseroth and Kreitzer were able to reverse Parkinson’s symptoms in mice. Deisseroth also discovered a brain circuit that controls mammals’ desire to interact socially. He and his team then used optogenetic techniques to trigger or inhibit social interactions between female mice. Previously, he induced and relieved symptoms of depression in mice.”

But Deisseroth’s work wouldn’t have been possible without “the discovery by Hegemann and Nagel of a cell-surface protein called channelrhodopsin in a single-celled algae that allowed the organism to sense and swim toward a light source. In the presence of blue light, they found, the protein formed a channel through which charged ions would flow, creating an electrical impulse. When channelrhodopsin was introduced to other cells, those cells also became light sensitive.”

Desisseroth himself recognised this soon after learning about the award: ““I couldn’t be happier because the trio that the committee picked spans the progression from the early algal explorations all the way to advanced neuroscience experiments, so this prize really captures the full journey of discovery,”

But as one of his colleagues put it: “Obviously their discovery was important — but it would have stayed on the shelf as some obscure, interesting finding that had almost no impact if Karl hadn’t figured out how to package it into viruses, get it into to cells, do the engineering to figure out how to get light into tissues, especially deep into the brain, and then showed the field how to use it.”

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