Hegemann, Nagel and Deisseroth share the medicine Nobel for switching neurons on with light

Science News puts the human brain at nearly 90 billion neurons joined by some 100 trillion connections ^[4]. That works out to roughly 1,100 connections per neuron on average ^[22]. Linking one behavior to one circuit inside that network takes a tool that can pick out specific cells. Abdel El Manira, a neuroscientist at the Karolinska Institute in Stockholm, described what the field wanted at the Oct. 5 announcement by the Nobel Assembly at Karolinska Institute ^[14][1]. "Neuroscientists dreamed of a neuronal switch, a tool to turn specific neurons on or off with great precision," he said ^[5].

The prize goes to biophysicists Peter Hegemann of Humboldt University in Berlin and Georg Nagel, and to Stanford neuroscientist Karl Deisseroth ^[2]. Their field, optogenetics, uses light to activate chosen cells and then watches how behavior changes ^[3]. The switch came out of basic work on an alga's eye spot ^[6]. "They had just discovered the switch neuroscientists had long dreamed of," El Manira said ^[8].

Deisseroth's experiments ran in two stages, and I like the design because each stage answered its own question. His group first put the channelrhodopsin gene into cultures of rat nerve cells, and the cells reacted to light instantaneously ^[9]. That showed a protein from an alga could drive mammalian neurons in a dish. Only then did the team move to living mice, adding the gene to brain cells and running optical fibers through the skull to carry blue light in ^[10].

The whisker result is an intervention. Recording which neurons fire while an animal moves shows two things happening together. Turning a defined circuit on and watching the whisker move tests whether the circuit drives the movement, and Science News says this is the ability the technology gave researchers ^[21]. "The technology, which soon became known as optogenetics, transformed neuroscience," El Manira said ^[11].

He added that the method "has also helped reveal how brain circuits are disrupted, with implications for conditions such as blindness, depression and dementia" ^[12]. The clinical example Science News gives is improved vision in some patients with retinitis pigmentosa, a disease that degrades the retina's light-sensing cells ^[13]. The article does not say how many patients were treated or how much their sight improved. The founding demonstration was in mice. For depression and dementia, the word El Manira used was implications ^[12].

The physics prize, in Science News's account, is for detecting an ultra-elusive subatomic particle from beyond the solar system ^[15]. That particle is the neutrino, and catching neutrinos from outside the solar system had been a goal of scientists for decades ^[17]. Science News credits physicist Francis Halzen with leading the creation of IceCube, the Antarctic observatory built to do it ^[19].

Science News describes the chemistry prize as a solution to "one of the most enduring puzzles in all of organic chemistry" ^[20].