How algae gave scientists a light switch for brain cells
Introducing light-sensitive proteins into selected neurons allows researchers to investigate how neural circuits influence behaviour (© The Nobel Committee for Physiology or Medicine)
A mouse enters a chamber where it has never received an electric shock. Researchers shine light onto a small group of genetically modified cells in its brain. The animal freezes.
Those cells had been active during an earlier frightening experience. Reactivating them prompted a defensive response in a different setting, providing evidence that the researchers had accessed part of the memory’s physical trace.
The experiment, reported in 2012, illustrates what makes optogenetics so compelling. The technique uses genetically introduced light-sensitive proteins to activate or suppress selected cells. By intervening in particular circuits, scientists can investigate how nerve cells help shape memories, feelings and behaviour, rather than simply watching them become active.
The discoveries that made such experiments possible earned Karl Deisseroth, Peter Hegemann and Georg Nagel the 2026 Nobel Prize in Physiology or Medicine, announced on 5 October. Their work on light-gated ion channels and optogenetics has transformed brain research and opened an experimental route to restoring sight.
The molecular machinery came from a single-celled alga responding to light.
How optogenetics helps trace memories
A memory leaves changes in networks of neurons. Establishing which cells contribute to its recall is far more difficult than seeing which brain regions become active.
In the 2012 study, Xu Liu, Steve Ramirez and colleagues labelled a population of cells in the mouse hippocampus, a region involved in memory, that became active during fear learning. The cells were made to produce channelrhodopsin-2, a light-sensitive protein.
Control experiments helped establish that the freezing depended on reactivating cells associated with fear learning, rather than illumination alone. The result supported the idea that the population formed part of a memory trace, sometimes called an engram.
Freezing provided behavioural evidence of recall, not a readout of the animal’s subjective experience. The achievement was to connect a defined group of cells with a specific memory-associated response.
Following brain circuits behind anxiety
Optogenetics also helped researchers move beyond broad descriptions of brain regions as centres for particular emotions.
The amygdala, for example, is often associated with fear. Yet it contains different populations and connections that can contribute differently to behaviour.
In a 2011 study, Kay Tye and colleagues targeted connections from the basolateral to the central amygdala. Activating this pathway made mice spend more time in exposed areas of a maze and an open arena, behaviour interpreted as reduced anxiety. Inhibiting the pathway produced the opposite effect.
The finding showed why the wiring matters. Stimulating an entire region can obscure the distinct contributions of the circuits within it.
These are animal experiments, with behavioural measures rather than direct reports of feelings. Their value lies in identifying mechanisms relevant to neurological and psychiatric research, rather than demonstrating a ready-made treatment for human anxiety.
Activating a pathway tests whether it can influence a response; suppressing it helps establish whether it is needed under the conditions tested. Those are different questions, and optogenetics can address both.
How algal proteins make neurons light-sensitive
None of these experiments would work simply by shining a torch at an ordinary neuron. The cells first need biological machinery that responds to light.
Hegemann investigated how Chlamydomonas reinhardtii, a single-celled green alga, senses illumination and adjusts its swimming. Working with Nagel and colleagues, he helped uncover channelrhodopsins: proteins that open a passage through the cell membrane when illuminated.
Charged particles, or ions, flow through that passage, changing the cell’s electrical state. Experiments showed the protein could also work in other cells.
Neurons were an especially intriguing destination. Their electrical impulses depend on ions crossing their membranes. Introducing an algal light-sensitive channel offered a way to influence that process.
In 2005, a team including Edward Boyden, Feng Zhang, Ernst Bamberg, Nagel and Deisseroth demonstrated millisecond-scale optical control of mammalian neurons. Two years later, Deisseroth and collaborators demonstrated optical control in living mouse brains.
Genetics supplied the switch to selected cells; light supplied the trigger. Other proteins subsequently enabled researchers to suppress activity.
Precision takes engineering
Electrical stimulation already allowed scientists to influence brain activity, but can recruit a mixture of nearby cells and nerve fibres. Optogenetics added genetic selectivity: chosen populations could respond to illumination even when surrounded by cells without the light-sensitive protein.
That precision depends on successful gene delivery and targeting. Light must also reach the intended tissue at an appropriate wavelength and intensity.
Brain tissue scatters and absorbs light, so experiments targeting deep structures often use implanted optical fibres. Miniature emitters and advanced optical systems offer other ways to deliver stimulation.
Too much illumination can heat tissue, and artificial firing patterns may differ from natural activity. Careful controls are essential. The compelling behavioural result depends on a substantial amount of biological and optical engineering.
Can optogenetics help restore vision?
For a blind patient in an experimental study, the consequence was more tangible: with special goggles, he could locate and reach for objects on a table.
Researchers led by José-Alain Sahel and Botond Roska reported the partial recovery of visual function in 2021. The patient had retinitis pigmentosa, a group of inherited disorders that progressively damage light-detecting photoreceptors.
The treatment introduced instructions for a light-sensitive protein called ChrimsonR into surviving retinal ganglion cells. Goggles captured the scene and projected patterned amber light onto the treated retina.
After training, the patient could perceive, locate, count and touch objects in tests. These abilities were not demonstrated without the goggles. The intervention bypassed lost photoreceptors; it did not rebuild them or restore normal sight.
Clinical development has since broadened. Nanoscope Therapeutics reported improved visual acuity in its randomised, sham-controlled RESTORE trial of MCO-010, whose analysed population comprised 27 participants. Its approach targets surviving retinal bipolar cells and is designed to respond to ambient light.
In September 2026, the company announced four-year follow-up data for a conference presentation, reporting sustained visual acuity gains. These company-reported results extend the evidence beyond a single patient, but require assessment alongside complete trial data. Better performance on a vision test does not by itself establish how independently someone can navigate everyday life.
From experiments to better treatments
The path from controlling a mouse’s neurons to treating a person remains demanding. Gene delivery, immune responses and long-term expression all require scrutiny.
Yet patients need not receive a light-sensitive protein to benefit from optogenetics. Identifying circuits involved in symptoms can suggest targets for medicines or other forms of stimulation.
The most far-reaching achievement may be the ability to ask a better question. When particular cells become active, are they accompanying an experience, or helping produce it? A protein from an alga gave scientists a way to begin finding out.
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