How does the brain decide which movement to make? Why do we sometimes freeze in fear and at other times flee? And how can memories change when we encounter new experiences?

For decades, neuroscientists have used a variety of approaches to investigate how different brain regions contribute to behavior, including stimulating or silencing them. Optogenetics has taken these efforts to a new level, allowing researchers to control the activity of specific types of neurons with unprecedented precision in time. This has opened up new possibilities for understanding how neuronal circuits shape behavior.

The technique, recognized by the 2026 Nobel Prize in Physiology or Medicine, awarded to Karl Deisseroth, Peter Hegemann and Georg Nagel, uses light-sensitive proteins to make nerve cells respond to light. Combined with other methods that allow these proteins to be introduced into specific types of neurons, optogenetics allows researchers to precisely control when and where particular neuronal circuits are activated or silenced.

At the FMI, this approach is helping scientists address some of neuroscience's most fundamental questions.

The brain's movement controllers
Every time we reach for a cup or pick up an object, our brain orchestrates a complex sequence of movements. In a 2025 study, researchers led by Silvia Arber investigated how neurons deep within the brain help control these actions.

By recording and manipulating neuronal activity in mice reaching for food, they discovered that particular neurons act through highly specific and dynamic signals, allowing certain movements to proceed while suppressing others with remarkable precision.

Using optogenetics, the team tested directly how these neurons contribute to movement. The findings offer new insights into the brain circuits affected by movement disorders such as Parkinson's disease.

“The extreme temporal precision with which optogenetic tools can be used, paired with the possibility to target them to very specific neurons, allows us to address all questions in the field of motor control with extreme acuracy, both in time and space,” Arber says. “This is key to understand how movement is generated, because movement is fast, precise and adaptive.”

Freeze or flee
When faced with danger, an animal may freeze in place or make a rapid escape. What determines which response it chooses? Andreas Lüthi's group has used optogenetics to investigate this question.

In experiments with mice, the researchers identified two populations of neurons in the amygdala, a brain region involved in processing fear. Activating one population triggered freezing, while activating the other promoted flight. Their findings revealed how interactions between specific groups of neurons help the brain select different responses to a threat.

The group has also used optogenetics to investigate other aspects of learning and behavior. In one study, the researchers identified specific neurons that help the brain learn from unexpected, important events. In another, they uncovered how patterns of neuronal activity in the amygdala help guide goal-directed behavior, such as pursuing a reward.

How the brain rewrites memories
Memories are not fixed recordings of the past. They can change as we gain new experiences, allowing us to adapt when circumstances change. Johannes Felsenberg's group investigates this flexibility using fruit flies, whose relatively simple brains allow researchers to study memory circuits in detail.

The team combines behavioral experiments, brain imaging and optogenetics to investigate how individual neurons contribute to learning and memory updating.

In research published earlier this year, the group found that when fruit flies encountered a familiar sugar reward again, memories previously associated with that reward could lose their influence over behavior without being completely erased.

Beyond basic research
Optogenetics is also showing promise in clinical applications. In a recent study, an international team co-led by former FMI group leader Botond Roska, now at the Institute of Molecular and Clinical Ophthalmology Basel, showed that an optogenetic therapy was safe in ten patients with advanced retinal degeneration, with several regaining some aspects of visual function.

Much remains to be discovered about the brain's complex networks, but optogenetics continues to provide FMI researchers with powerful new ways to investigate how they function.