Optogenetics: how light helps us understand the brain

The 2026 Nobel Prize in Medicine and new perspectives in the treatment of neurological and psychiatric conditions

What if we could identify the neurons involved in an emotion, a memory or a behaviour, and change their activity using light?

This has become possible thanks to optogenetics, a method that combines genetic techniques with light stimulation to control the activity of certain neurons and study how brain circuits work.

The discovery opens new perspectives for understanding depression, addiction and some major neurodegenerative diseases, such as Parkinson’s and Alzheimer’s. Identifying the mechanisms involved could, in the future, help develop more precise treatments.

The importance of this achievement was recognised in October 2026, when Karl Deisseroth, Peter Hegemann and Georg Nagel were awarded the Nobel Prize in Physiology or Medicine, for their discoveries concerning light-gated ion channels and the development of optogenetics.

A discovery that began with an alga

Optogenetics has its origins in the study of single-celled algae that can react to light.

Peter Hegemann, Georg Nagel and their colleagues helped identify proteins called channelrhodopsins. These work like microscopic channels that open in response to light, letting ions pass through the cell membrane and changing the cell’s electrical activity.

Later, Karl Deisseroth and his colleagues showed that such proteins could be used to control the activity of neurons.

Light thus became not only a means of observation, but also a tool for experimental intervention in how the brain works.

How does optogenetics work?

The brain’s billions of neurons communicate through electrical and chemical signals, forming networks involved in memory, emotion, motivation and behaviour.

Using genetic techniques, researchers can introduce light-sensitive proteins into specific groups of neurons. Pulses of light can then activate or inhibit these neurons, depending on the protein used, with millisecond precision.

The value of the method lies in being able to observe not only which brain regions are active during a behaviour, but also what happens when the activity of the neurons involved is changed in a controlled way.

This makes it possible to investigate cause-and-effect relationships between how neural circuits work and certain behaviours.

What can optogenetics tell us about brain disorders?

One of the method’s important contributions is identifying the circuits involved in psychiatric and neurological disorders, which points to possible directions for developing better-targeted treatments.

In depression, the symptoms cannot be explained only by changes in neurotransmitter levels. Circuits that regulate mood, motivation, the ability to feel pleasure and the response to stress are also involved.

The structures studied include the ventral tegmental area and the nucleus accumbens, connected through reward and motivation circuits, which are relevant to understanding anhedonia (a reduced ability to feel pleasure).

In animal experiments, selectively activating or inhibiting certain neurons in these circuits has changed depression-related behaviours, including interest in reward and the response to stress.

The results do not reproduce the full complexity of human depression, but they help identify mechanisms that could become targets for treatment.

In addiction, attention turns to the networks involved in reward, learning and behavioural control. Repeated use can change how these networks work, so that cues associated with the substance trigger an intense craving, even when the negative consequences are known.

In animal models, changing the activity of certain neural connections with optogenetics has influenced compulsive drug seeking and behaviours associated with relapse.

These results can guide the development of more precise interventions, without diminishing the importance of psychological and social factors in how addiction begins and develops.

Optogenetics also offers valuable insights into neurodegenerative diseases, especially Parkinson’s and Alzheimer’s.

In Parkinson’s disease, the loss of dopamine-producing neurons affects the circuits of the basal ganglia, which are involved in controlling movement. In experiments in mice, selectively stimulating certain neural pathways has improved some parkinsonian-like motor symptoms.

These observations help us understand motor circuits and can guide the refinement of neuromodulation methods, including deep brain stimulation.

In Alzheimer’s disease, a key question is whether memory problems arise only because stored information is lost, or also because it becomes difficult to retrieve.

A study published in Nature in 2016 showed that optogenetically activating neurons involved in forming memories allowed some information to be retrieved in mouse models of Alzheimer’s.

The result suggests that, at certain stages of the disease, some memories may become inaccessible without being completely lost. This finding does not show that memory can be restored in patients, but it opens new directions for research into cognitive mechanisms.

From the lab to treatment

One of the first experimental clinical applications of optogenetics was in ophthalmology.

In 2021, a study published in Nature Medicine described the partial recovery of some visual function in a patient with advanced retinitis pigmentosa, a degenerative disease of the retina.

After a light-sensitive protein was introduced into certain retinal cells, and with the help of special goggles, the patient was able, after training, to perceive and locate some objects.

Although sight was not fully restored, the result showed that the principles of optogenetics can be applied in humans.

In neurology and psychiatry, direct use is much more difficult. It would require safely introducing light-sensitive proteins into selected brain regions, delivering light in a controlled way and assessing the long-term effects.

At present, optogenetics is not a validated clinical treatment for depression, addiction, Parkinson’s or Alzheimer’s.

However, identifying more precisely the circuits involved in certain symptoms could help refine neuromodulation methods already in use, such as transcranial magnetic stimulation and deep brain stimulation, which work through mechanisms different from optogenetics.

In the long term, this knowledge could also guide the development of medicines that act more selectively on the biological mechanisms of disease.

A new perspective on the brain

Optogenetics has transformed research into neural circuits, making it possible to investigate directly how they contribute to memory, emotion and behaviour.

For neurology and psychiatry, this approach matters in a field where similar clinical signs can have different biological mechanisms, and the response to treatment varies from person to person.

A more precise understanding of these mechanisms could help develop individualised interventions, without reducing the complexity of mental disorders to the isolated activity of a few neurons.

The greatest contribution of optogenetics to the medicine of the future may be not treating the brain directly with light, but identifying more precisely the mechanisms of disease and the ways in which we can intervene.

A discovery that began with the study of single-celled algae has thus become a fundamental tool of modern neuroscience, opening new perspectives for understanding and treating neurological and psychiatric conditions.

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Sources and further reading

1. The Nobel Prize in Physiology or Medicine 2026. The Nobel Assembly at Karolinska Institutet.
2. Boyden ES et al. Millisecond-timescale, genetically targeted optical control of neural activity. Nature Neuroscience, 2005.
3. Tye KM et al. Dopamine neurons modulate neural encoding and expression of depression-related behaviour. Nature, 2013.
4. Kravitz AV et al. Regulation of parkinsonian motor behaviours by optogenetic control of basal ganglia circuitry. Nature, 2010.
5. Roy DS et al. Memory retrieval by activating engram cells in mouse models of early Alzheimer’s disease. Nature, 2016.
6. Sahel JA et al. Partial recovery of visual function in a blind patient after optogenetic therapy. Nature Medicine, 2021.