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 that allows scientists to turn individual nerve cells on or off using beams of light.
Per Svenningsson, chair of the Nobel Committee for Medicine, stated, “Optogenetics provides opportunities for mapping the brain in a way that we could once only dream of.” This technique enables precise study of the living brain, aiding researchers in understanding the functions of the nervous system and various neurological diseases and disorders.
The prize also highlights the convergence of different biological disciplines, as the findings that led to optogenetics emerged from microbiology research. In the late 20th century, Peter Hegemann began studying how the single-celled alga Chlamydomonas detects and reacts to light. Previous research had shown that Chlamydomonas possesses an “eye spot,” a small orange dot containing a light-sensing molecule called retinal.
Hegemann used tiny electrodes to measure the electrical signals generated by the alga, discovering that it could produce an electrical impulse approximately 0.5 milliseconds after receiving light, which is 20 times faster than the human eye's response time of at least 10 milliseconds.
Hegemann proposed that light detection in the alga resulted from a simpler process than that in the human eye, suggesting that the eye spots contained a protein that detected and responded to light, likely opening as a channel for ions. His hypothesis, proposed in the early 1990s, generated controversy as no ion channels had been documented to respond to light independently.
To test his theory, Hegemann attempted to isolate the light-sensitive proteins from the eye spot, but they became unstable when removed from their natural environment. Later, Japanese researchers sequenced the complete DNA of Chlamydomonas, allowing Hegemann’s team to identify two genes that could produce proteins with the expected characteristics of a light-sensing channel.
Georg Nagel verified the function of these genes by introducing copies into frog eggs, which began producing the corresponding proteins localized to the cell membranes. When exposed to light, both proteins functioned as ion channels. Nagel named these genes channelrhodopsin-1 and channelrhodopsin-2, with ChR2 opening particularly quickly at 0.2 milliseconds, explaining the rapid light reaction observed in Chlamydomonas.
When introduced into mammalian cells, which typically do not respond to light, the cells generated an electrical signal when illuminated, garnering interest from neuroscientists.
Ion channels play a crucial role in various cell types, especially in the nervous system, where they mediate the electrical impulses neurons use to communicate. Controlling ion channels allows for the control of neuron activity.
Karl Deisseroth sought a method to toggle the activity of specific nerve cells in a living brain, aiming to enhance understanding of brain functions and explore treatments for conditions such as depression and schizophrenia. After discovering ChR2, he obtained the DNA sequence from Nagel to introduce it into rat nerve cells. The neurons produced ChR2 and reacted to blue light by sending electrical impulses, a pivotal result achieved in 2005 that established ChR2 as a neuroscience tool.
In subsequent years, Deisseroth, Hegemann, and Nagel collaborated to identify additional proteins that could activate or deactivate neurons using different light wavelengths. This toolkit enables researchers to design experiments where one group of neurons is activated by one wavelength and another group by a different wavelength.
The term optogenetics was coined in 2006 and has since been applied in various studies. According to the Nobel Assembly at the Karolinska Institute, “Using optogenetics, researchers have been able to reveal neural circuits governing specific memories, feelings, and behaviors relevant for neurological and psychiatric disorders. In clinical medicine, researchers are using the method in attempts to restore sight in people with visual impairment.”