What could a tiny green alga swimming towards light possibly have to do with the human brain?At first glance, almost nothing; yet a scientific journey that began with researchers trying to understand how a microscopic alga senses light, eventually led to a technology that allows scientists to control selected nerve cells with light and it subsequently changed the way brain can be studied. Recently, it earned science’s highest recognition as the Nobel Prize in Physiology or Medicine 2026 has been awarded to Karl Deisseroth (Stanford University, USA), Peter Hegemann (Humboldt University, Germany) and Georg Nagel (University of Wurzburg, Germany) for discoveries leading to optogenetics.

Beyond the achievement itself, there is a wonderful story about how science actually progresses. Important discoveries do not always begin with attempts to cure a disease or invent a technology. Sometimes they begin with somebody becoming curious about something in nature and asking a seemingly simple question: How does this work? Questions may initially relate to seemingly unrelated fundamental biology, but can ultimately lead to important discoveries directly related to humans and other beings.

Following an alga towards the lightChlamydomonas is a microscopic, single-celled green alga. Like many organisms, it can respond to its environment - in this case, to light. Scientists wanted to understand – how?That investigation led Peter Hegemann, Georg Nagel and other researchers to proteins called channelrhodopsins. These proteins sit in the cell membrane and respond to light by allowing electrically charged ions to pass through.To a non-scientist, this might sound like an interesting but rather specialised detail about the biology of an alga. But scientists saw another possibility. A friend of mine working at University of Frankfurt during 2003-04 told me of his memories from the time when the researchers from Prof. Nagel’s team were conducting Electrophysiology experiments to understand the nature of these proteins and then figured these were light sensitive channels.Nerve cells also communicate through changes in electrical activity. So what would happen if this light-sensitive protein could be placed inside a neuron? Could one, quite literally, switch a nerve cell on with light?

The question was intriguing and the idea worked.Karl Deisseroth and colleagues demonstrated that channelrhodopsin could be introduced into organismal neurons and used to control their firing with extraordinary precision.From this grew optogenetics - a combination of genetics and optics that allows particular populations of cells to be controlled using light. The implications were enormous.

Imagine trying to understand a complicated electrical circuit by watching it from outside. You may see which components become active, but that does not necessarily tell you what each one actually does. Now imagine being able to select one component, switch it on or off, and observe what changes.Optogenetics gave neuroscientists something approaching that ability in the living nervous system.

Researchers could begin asking: Which neurons initiate a particular movement? Which circuits influence reward or fear? What happens when a particular........

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