THE CONVERSATION: How pond algae led to a Nobel and new ways

Three researchers were honoured with the prize in physiology or medicine for revealing potential new ways to control nerve cells, and it all started with a sensible question. By Robert Lucas 11 Oct 2026 From left: Karl Deisseroth, Peter Hegemann and Georg Nagel, winners of the 2026 Nobel prize in physiology or medicine. (Photos: Hidenori Nagai / AP; Soeren Stache / dpa Picture-Alliance; Christian Wiese / Uni Würzburg / dpa Picture-Alliance) Dive Deeper Speed Read Summary Listen Dive Deeper Scientists who worked out how to control brain cells with light have won this year’s Nobel prize in physiology or medicine.

Karl Deisseroth, Peter Hegemann and Georg Nagel were honoured for their research into “light-gated ion channels and optogenetics”. Hegemann, at Humboldt University of Berlin, and Nagel, at the University of Würzburg, wanted to understand how a tiny, single-celled alga called Chlamydomonas senses light. Light-sensing is not unique to animals with eyes: organisms throughout the living world use light to detect their surroundings and respond to changes in their environment.

Even single-cell organisms have proteins that respond to light. These proteins are used to move towards or away from light, generate energy and respond to the various demands of a 24-hour day. Hegemann and Nagel discovered that Chlamydomonas has a beautifully ingenious mechanism of light detection that relies on a single protein called channelrhodopsin.

Channelrhodopsin is built into the outer membrane of the algal cell. Part of the protein faces the water outside the cell and part faces the inside. The protein also contains a small molecule called retinaldehyde, which is able to absorb light.

When light hits the retinaldehyde inside channelrhodopsin, it changes shape, which makes the channelrhodopsin protein change shape too. This change opens a tiny passage through the cell membrane.

Positively charged particles, including sodium, can then flow from the water outside the alga into the cell. This movement of charged particles sends a signal inside the alga that helps it to swim.

How fantastic to have solved such an interesting biological question, but why the Nobel prize in physiology or medicine? The answer lies in the way nerve cells work.

Nerve cells use the movement of charged particles (called “ions”) across their membranes to control their activity. When positively charged particles flow into a nerve cell, they can make it more active.

The researchers realised that if they could put channelrhodopsin into nerve cells, they might be able to switch those cells on simply by shining a light on them. That is exactly what Hegemann, Nagel and the third Nobel-prize winner, Deisseroth, a psychiatrist and bioengineer at Stanford University in California, went on to do.

Switching on nerve cells with light The ability to control nerve cells with light is called optogenetics. It has become a powerful research tool because scientists can use it to switch specific groups of nerve cells on and off and see what happens.

First, scientists deliver the gene for channelrhodopsin to the nerve cells they want to study. The gene is usually carried into the cells by a virus that has been altered so that it cannot cause disease.

The cells then make the channelrhodopsin protein, which makes them respond to light. In animals such as mice, scientists can shine light into the brain through a thin optical fibre.

When the light reaches the cells, channelrhodopsin opens and the cells become active. Nearby nerve cells that do not contain the protein are unaffected.

Medical Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult with qualified healthcare professionals for medical decisions and treatment options.