The Fertility of an Idea: tracing the discovery lineage of optogenetics

10-27-2026Part of the Amplify Writing Fellowship

When you enter a very dimly lit room, at first the details are muted, and then slowly the objects and space around you start to reveal themselves. You see the edge of a table, the glint of your toaster, folds in a curtain, the outline of your own hand. Deep in the rod cells at the back of your eye, a protein called rhodopsin is catching that faint light and turning it into a signal you can see.

Earlier this month the 2026 Nobel Prize in Physiology or Medicine went to Karl Deisseroth, Peter Hegemann and Georg Nagel "for their discoveries concerning light-gated ion channels and optogenetics", a technique that lets you turn specific neurons on and off with pulses of light. This Nobel winning technique was made possible due to a type of rhodopsin protein that came not from the human eye, or from any animal at all, but instead from a single-celled green alga. The most precise tool neuroscience has for controlling the neurons in your brain came from a creature that doesn’t even have one.

The discovery process of how this field-opening protein made its way from the soil to the brain doesn’t follow a straight and predictable journey. Instead, it unfolds as a series of seemingly disparate scientific contributions and curiosities. The path runs from a microbe that lives on sunlight in brine, through frog eggs in Frankfurt, an open catalogue of genes in Japan, over thirty years and through fields that had nothing to do with neuroscience at all. It’s decidedly non-linear.

This is true of many important scientific discoveries. A lot of the critical pieces on the discovery trail could look modest or unrelated when they were initially developed. They lay frozen in the collective scientific consciousness, sometimes for decades, until someone with a different perspective picked them up and asked questions far from those that led to their inception.

This piece traces the discovery lineage of optogenetics, and shows how great scientific work grows the way living things do. Flowing across time, people, instruments, branching and borrowing, advancing through detours, delays, serendipity, and exchange. Along the way, the significance of a finding appears less in the question it answered than in how many directions it opened beyond itself. I call this the fertility of an idea.

Our journey begins with the salt-loving microbe, Halobacterium, which thrives in brine almost too salty for anything else to live in. These microbes grow so densely that they transform bodies of water into dreamy pink and purple pools. It was in 1971 when Dieter Oesterhelt and Walther Stoeckenius, studying this microbe, discovered bacteriorhodopsin.

Bacteriorhodopsin sits in patches of the microbe's membrane, coloured purple by the retinal – a light-absorbing molecule made from vitamin A – that it holds. Within a couple of years, Oesterhelt and Stoeckenius had shown that it uses light to pump protons across the cell membrane. Each time the light hit, it pushed a proton out of the cell, which was a simple way of turning sunlight into usable energy.

Soon enough, 6 years later, Yasuo Mukohata's group in Osaka found signs of a second light-driven pump in the same microbe, Halobacterium. The protein, later named halorhodopsin, was first assumed to be a sodium pump, but in 1982 Brigitte Schobert and Janos Lanyi showed it actually moves chloride. At the time, both bacteriorhodopsin and halorhodopsin belonged to the category of research dealing with how microbes make energy. They weren’t yet seen as potential tools for neuroscience, which would ultimately prove to take some time.

Even before the cross over into neuroscience, bacteriorhodopsin had already literally changed how biologists see proteins. It started with a problem: the electron microscope tends to destroy the very samples that it could give scientists the power to see. But in the purple membrane of the bacteriorhodopsin’s microbe, this protein happens to pack itself into a naturally regular lattice, repeating the same unit thousands of times. In 1975 (4 years after the discovery of bacteriorhodopsin) Richard Henderson and Nigel Unwin realized that they could use this lattice to their advantage. They turned the microscope’s beam down so low that each individual image was mostly noise, letting the regularity of the lattice do its work, and then combined the signal from thousands of identical copies into one clear picture.

Their model was the first three-dimensional picture of a protein made with an electron microscope, and it showed seven helices packed side by side, each one crossing the membrane. Henderson kept refining the approach, and by 1990 had a near atomic-resolution model.

This very same logic of averaging many noisy images of identical molecules grew into cryo-electron microscopy, which won the 2017 Nobel Prize in Chemistry. The discovery of bacteriorhodopsin in 1971 set off a chain no one could have foreseen.

And while bacteriorhodopsin was opening up a new way of seeing in biology, another line of inquiry was forming around what more these light-driven rhodopsin proteins could do and where else they might be found.

Peter Hegemann, who had worked on the light-driven protein halorhodopsin as a PhD student in Oesterhelt's lab, moved in 1985 to work with Kenneth Foster, who had just shown that the green alga Chlamydomonas senses and navigates by light using (a not yet specified) rhodopsin. In 1991, using a suction-pipette technique first developed in Moscow on a different alga, Hegemann's group recorded currents in the alga that appeared almost the instant the light did.

This speed was of particular interest because the rhodopsin in your eye isn’t nearly as fast as this. When light enters your eye, the rhodopsin works as a sensor rather than a switch and when it catches light it passes the news to a relay of other proteins, each one multiplying the message until there’s enough to change the cell’s electrical state. Every handoff along this relay takes time.

The currents in the alga came too quickly for anything like that…so how did they work? The simplest explanation was that there was no relay at all, and that in the alga the light sensor and the switch were the same protein. Instead of a sensor relaying information along, the rhodopsin would itself act as a light-gated channel that once triggered, would open up, letting charged particles flow through. This was a pretty compelling idea, however, no one had yet found a protein that displayed these properties.

Unbeknownst to them yet, the protein they were looking for was sitting in an open algal gene sequence library, published by Japan's Kazusa DNA Research Institute. Roughly thirty years after bacteriorhodopsin's discovery, Suneel Kateriya in Hegemann's group searched that catalogue for genes resembling bacteriorhodopsin. He found two candidates in the alga Chlamydomonas. Groups in Texas and Japan found the same two genes at almost the same time, but what nobody had yet shown was whether these proteins worked like light-gated channels that so far existed only as an idea.

As it happened, the way to find out and test the two candidates had already been developed years earlier to answer another question. It was in 1995 when Georg Nagel and Ernst Bamberg wanted to know how hard bacteriorhodopsin could push protons against a voltage – measuring the strength of its light-driven pump. Their solution was to express bacteriorhodopsin in frog oocytes, the immature egg cells of a frog, using a trick borrowed from developmental biology that had already crossed over into neuroscience. In solving their own problem, they also showed that a microbial rhodopsin could work in something as complex as an animal cell. Six years later, in another twist along the lineage of discovery, their work could be applied to a question about algal rhodopsins.

Hegemann, already familiar with this work in frog oocytes, and having worked with Bamberg on halorhodopsin in the 1980s, teamed up with both Nagel and Bamberg and sent them the two candidate genes that Kateriya had identified. Could these be the proteins they were looking for?

When Nagel and Bamberg expressed these two genes in frog oocytes, the proteins indeed turned out to be channels that opened in response to light! They named the first channelrhodopsin-1 and published it in 2002, and a year later described the second, channelrhodopsin-2, which let positively charged ions flood into the cell whenever light hit it. In that 2003 paper they also tried it in mammalian cells, and suggested it could be useful for manipulating the membrane potential of mammalian cells.

These were biophysicists interested in a very particular research area: how proteins move ions across membranes. Despite such a seemingly narrow focus, they had, perhaps without quite meaning to, opened the door to a field that didn’t yet exist.

Over in neuroscience, researchers really wanted the ability to switch one type of neuron on or off without triggering any other nearby cells. By the late 1990s some researchers were wondering whether light might be the answer.

One of the early genetic light-control attempts came in 2002 when Gero Miesenböck's group made neurons light-sensitive by giving them a set of genes borrowed from the light-sensing cells of fruit flies. They were the first to prove that the idea was possible. But the system they built was, in effect, similar to the relay from your eye: they had several proteins working together, each passing the message on to the next, and every handoff taking time. What neuroscience was still lacking at this time was something simple, fast, and self-contained.

Over at Stanford, Ed Boyden had read the channelrhodopsin paper and together with Karl Deisseroth who was just setting up his own lab, asked Nagel for the gene.

Feng Zhang, a graduate student working with Deisseroth, used a virus to deliver this gene into rat neurons growing in a dish. Then came the pivotal experiment where Boyden pulsed blue light onto one of the prepared neurons and recorded a fast, precise electrical spike in response to most of the flashes. These findings were published in 2005 and within a few years, channelrhodopsin became the basis of a new way to control neural activity.

As it turned out, they weren't the only ones putting channelrhodopsin into neurons. When the foundations and preconditions of an idea are in place, the same discovery has a habit of appearing in more than one place at once. The sociologist Robert Merton called these “multiples” and thought they were the rule rather than the exception.

So it’s not so surprising then, that in Detroit, Zhuo-Hua Pan at Wayne State University had been trying to restore sight by making the surviving cells of a degenerated retina respond to light. In early 2004, months before Boyden's experiment, he observed retinal neurons – carrying the very same channelrhodopsin – respond to light. He struggled to get his work published, before his paper was finally accepted in 2006.

While Pan waited for his paper to be accepted, the technique was already spreading. Within four months of the 2005 Stanford paper, labs in Ohio, Frankfurt and Sendai had channelrhodopsin working in chick spinal cords, worms and mouse brain slices. In 2006, Deisseroth and his colleagues gave the growing approach a name, optogenetics: control by light, written into cells by their genes.

The salt pond had one more gift to give us. Halorhodopsin, the second protein found in 1977 in Osaka, turned out to be very valuable 30 years later, when a version from a related microbe became the off switch. This turned out to be another “multiple” found independently by Ed Boyden’s lab and Deisseroth’s, letting neuroscientists silence neurons with yellow light.

Soon, light could be delivered through thin optical fibres into the brains of mice that were free to move, and in 201