It is fascinating to consider how this intricately folded organ, tucked away inside our heads, can give rise to a memory, shape an emotion, influence a decision or direct the body's movements. Inside it, billions of nerve cells communicate through a complex network of connections. Their activity underlies our ability to think, remember, perceive the world and experience emotions. Yet understanding how the activity of specific nerve cells and the circuits they form contributes to memory, emotion and behaviour has long been a central question in neuroscience.
The discoveries recognised by this year's Nobel Prize in Physiology or Medicine have given scientists a powerful new tool to investigate that question. Karl Deisseroth, Peter Hegemann and Georg Nagel were awarded the 2026 prize for discoveries concerning light-gated ion channels, which helped pave the way for optogenetics.
Optogenetics uses light-sensitive proteins to make selected cells responsive to light, allowing researchers to control their activity and investigate how specific neurons and neural circuits contribute to brain function and behaviour.
How optogenetics helps identify neuronal function
For decades, neuroscientists have developed increasingly sophisticated ways to observe activity in the living brain. However, identifying which neurons become active during a particular experience does not necessarily establish whether that activity causes it. Optogenetics offers researchers a way to investigate that relationship more directly.
The technique involves introducing genes that encode light-sensitive proteins into selected cells, allowing researchers to control their activity using light. Depending on the proteins used, researchers can activate or inhibit neuronal activity and observe how these changes affect the functions or behaviours being studied.
Dr Mohammad Nami, associate professor and department chair at the School of Health Sciences & Psychology at Canadian University Dubai, described the Nobel-recognised work as a major conceptual shift in neuroscience.
“It moves us from asking ‘What brain activity accompanies a mental process?’ toward ‘What happens to that mental process when we selectively intervene in the circuitry?’” he said.
The distinction is significant because a single brain region can contain different populations of neurons with different, sometimes opposing, functions. Observing an entire region may not reveal which cells contribute to a particular process. By targeting selected populations, optogenetics allows researchers to investigate how specific neurons contribute to a function and how manipulating them affects the wider circuit.
Understanding stress susceptibility
Optogenetics has allowed researchers to investigate how specific neural circuits contribute to behaviour, including responses to stress.
Dr Dipesh Chaudhury, associate professor of biology at New York University Abu Dhabi, said his team identified a brain circuit that showed altered daily patterns of activity, including elevated daytime activity.
In a 2021 study, the researchers stimulated this circuit during mild stress and found that the mice developed behaviours associated with stress susceptibility. “Optogenetics allows us to understand how abnormal activity in specific brain circuits affects behaviour,” Chaudhury said.
The experiment allowed the researchers to test whether changing activity in the circuit could influence the mice's response to stress, rather than simply observing an association between the two.
Potential clinical applications
While optogenetics remains primarily a research tool, the knowledge it generates could help guide the development of future treatments for neurological and psychiatric disorders.
Nami said its immediate importance lies in helping researchers understand disease mechanisms and identify potential targets for treatment, rather than providing a direct therapy in itself.
Chaudhury similarly noted that most research using optogenetics is still focused on understanding the brain, although the findings are beginning to inform the development of potential treatments.
He identified vision restoration as the most promising clinical application, pointing to research in which optogenetic therapy produced partial recovery of visual function in a patient with severe retinal disease.
For conditions such as depression, Parkinson's disease and epilepsy, Chaudhury said the technique's main contribution at present is helping researchers identify relevant neural circuits and inform possible treatments. These remain promising research directions rather than established optogenetic therapies.
Nami cautioned that, while optogenetics allows researchers to manipulate specific neurons with precision, understanding how their activity contributes to complex thoughts, emotions and behaviour remains a much broader challenge.
“Precision of intervention should not be confused with completeness of explanation,” he said.
As research continues, optogenetics could help scientists build a clearer picture of how neural circuits contribute to brain function and disease, bringing them closer to identifying targets for future treatments.