STOCKHOLM (AP) — The Nobel Prize in medicine was awarded Monday to three scientists who created a tool using light to help unravel how the brain works.

Karl Deisseroth, 54, Peter Hegemann, 71, and Georg Nagel, 73, have carried out research into light-gated ion channels and optogenetics.

The Nobel Assembly lauded their work and said the method is now being used in laboratories around the world to reveal the brain’s mysteries.

The assembly said Deisseroth is based at Stanford University in California, while Hegemann is at Humboldt University in Berlin and Nagel at the University of Würzburg, also in Germany.

Optogenetics opened what the Nobel assembly called a new era in neuroscience, the discovery of a light-controlled switch to turn on and off nerve cells and circuits in the brain to better learn how it works — to start unraveling the pathways that lead to behavior and disease.

It started when Hegemann explored how a single-celled type of green algae can swim toward light. He and Nagel discovered a particular protein that, when illuminated by blue light, opens a channel to create an electrical impulse. Putting that protein into other cells makes them light-sensitive.

Deisseroth then worked with the gene that controls that protein to create a light-controlled switch for nerve cells in the brains of living mice.

“It’s a very precise set of tools for doing experiments about how the brain works that are pretty hard to do any other way,” said the University of Pittsburgh’s Jeremy Berg. He was at the National Institutes of Health in the early 2000s when it awarded Deisseroff major funding for “this vision of optogenetics that was pretty much spot-on the way it played out.”

One winner had just gone to bed

Deisseroth, a self-described night owl, said he was up late in his Northern California home working on papers and emailing his students. He had just gone to lie down when he got the call from the Nobel assembly.

“No real sleep was achieved,” he told The Associated Press in a phone call an hour after the announcement.

He said the next task on his to-do list was to pack school lunches for his children, who were still sound asleep.

“That’s my one obligation I have in the next few hours, to make sure I make their sandwiches,” he said.

Thomas Perlmann, the secretary of the medicine committee, said he was able to reach all three winners Monday. The AP's efforts to reach Hegemann and Nagel were not immediately successful.

Medicine prize kicks off Nobels week

The prize was announced at the Karolinska Institute in Stockholm, kicking off Nobels week. The prize money this year is 12 million Swedish kronor (about $1.2 million).

Last year, the prize went to three scientists researching the immune system.

Monday's medicine prize is followed by the physics prize on Tuesday, chemistry on Wednesday and literature on Thursday.

After Friday’s peace prize is awarded, the Nobel Memorial Prize in Economic Sciences will be announced on Oct. 12.

The prize money this year is 12 million Swedish kronor (about $1.2 million), whether for an individual, small group of laureates or organization.

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Neergaard reported from Washington and Ramakrishnan reported from New York. Stefanie Dazio in Berlin contributed to this report.

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AP Nobel Prizes: https://apnews.com/hub/nobel-prizes