The Science Behind the Nobel-Winning Technology That Controls Neurons With Light

The Karolinska Institute awarded the 2026 Nobel Prize in Medicine to researchers Karl Deisseroth of Stanford University, Peter Hegemann of Humboldt University in Berlin, and Georg Nagel of the University of Würzburg. Their discoveries led to the development of optogenetics, a technique where scientists can turn individual nerve cells on or off using beams of light.

According to Per Svenningsson, chair of the Nobel Committee for Medicine, “Optogenetics provides opportunities for mapping the brain in a way that we could once only dream of.” No other technique allows for such precise study of a living brain, helping researchers better understand the functions of our nervous systems as well as various neurological diseases and disorders.

But this prize is not just a celebration of neuroscience. It also serves as a triumphant example of what can happen when different disciplines of biology converge, as the findings that served as the basis for the development of optogenetics emerged from research in microbiology.

At the end of the last century, Peter Hegemann began a series of studies to understand how the single-celled alga Chlamydomonas is able to detect and react to light. Previous research documented that Chlamydomonas has an “eye spot,” a small orange dot on its surface that contains a light-sensing molecule called retinal.

Hegemann used tiny electrodes to measure the electrical signals generated by the alga and to expand our understanding of this structure’s rapid response. The scientist discovered that the organism was capable of producing an electrical impulse about 0.5 milliseconds after receiving light. This response time is 20 times faster than that of the human eye, whose light detection process takes at least 10 milliseconds.

Hegemann suggested that light detection in the alga must be the result of a much simpler process than that identified in the human eye. In the early 1990s, he proposed that the eye spots contained a protein that both detected the light and responded to it, likely opening as a channel to let ions through. At the time, this hypothesis sparked controversy. Many ion channels had been documented up to that point, but none could respond to light on their own.

To test his theory, the scientist attempted to isolate the light-sensitive proteins from the eye spot. However, when removed from their natural environment, these proteins became unstable. Later, a group of Japanese researchers sequenced the complete DNA of Chlamydomonas, which allowed Hegemann’s team to identify two genes that would create proteins with the expected characteristics of a possible light-sensing channel.

Georg Nagel took the next step of verifying the function of the genes. He introduced copies of each of the identified genes separately into different groups of frog eggs. The eggs began to produce the corresponding proteins, which eventually localized to the cell membranes. Nagel then turned on the lights.