須田桃子～ノーベル生理学・医学賞を受賞した「光遺伝学」

How Suda Momoko Enjoys Nobel Prize Season

Science journalist Suda Momoko (須田桃子)—formerly a reporter in the science and environment section of the Mainichi Shimbun and deputy editor at NewsPicks before going freelance—says she never misses the official announcement videos and press releases during Nobel Prize season. The press releases come in both a popular version and a technical version, and comparing the two is one of her seasonal pleasures. On optogenetics, she noted that "it had been an anticipated topic for some time, but clinical applications hadn't started yet, which may be why it hadn't won before," and analyzed that the launch of several clinical studies likely gave it the push it needed this year.

News Commentary: Hokkaido Shimbun Reporter Detained in Russia

The episode also addressed the day's news: the detention of a Hokkaido Shimbun reporter in Sakhalin. Speaking as a former newspaper reporter, Suda expressed strong concern. Against Russia's claim that the reporter had been "gathering information on soldiers who participated in the Ukraine invasion," she countered: "That is a topic any journalist would naturally cover in the course of normal reporting." She criticized the release of footage of the arrest as "a human rights violation" and said her greatest worry was the chilling effect that repeated incidents like this would have on on-the-ground journalism. "I hope other reporters will not be intimidated," she said. "Press freedom is genuinely vital in guaranteeing the public's right to know."

What Is Optogenetics?

The main topic of the episode is optogenetics (光遺伝学), this year's Nobel Prize in Physiology or Medicine winner. Suda sums it up in one line: "a technology that can instantly switch only the targeted neurons in the brain on or off using light." The brain contains roughly 86 billion neurons, each connected to thousands—or even ten thousand—others through synapses, forming an enormously complex network. Changes in that network give rise to memory, emotion, and behavior, but until now there was no way to manipulate specific cells in isolation with precision. Like CRISPR-Cas9, which won the 2020 Nobel Prize in Chemistry, optogenetics has spread rapidly to neuroscience labs around the world and has become, in Suda's words, "an indispensable tool."

Origins: Pure Curiosity About Algae

Optogenetics began with pure scientific curiosity about why single-celled green algae swim toward light. German researchers Dr. Hegemann and Dr. Nagel studied how algae respond to light more than twenty times faster than the human eye and discovered the light-sensitive protein channelrhodopsin. When they introduced the gene into mammalian cells such as hamster cells, cells that normally have no response to light began responding to it.

Karl Deisseroth of Stanford University was the one who adapted this discovery for neuroscience. Searching for a method to precisely control neurons, he read the channelrhodopsin paper and immediately sensed its potential. In 2005 he demonstrated light-based control of rat neurons, and two years later reported success in the living mouse brain. The three researchers—Hegemann, Nagel, and Deisseroth—are this year's Nobel laureates.

Suda interviewed Deisseroth in 2018 when he received the Kyoto Prize. Two things stayed with her: that he had paid no attention to competing labs, believing he was essentially the only one working on the problem; and his strong emphasis on cross-disciplinary fusion. The technology combines optics, genetic manipulation, and viral vector techniques—a product of multiple fields converging. His experience as a psychiatrist treating patients was also a central motivation. MIT's Susumu Tonegawa (利根川進), who passed away in July of this year, collaborated with Deisseroth and in 2012 published a landmark paper using optogenetics to identify which neurons are required for specific memories—a paper the Nobel Committee cited in its press release.

Clinical Promise and the Ethics of Emotion Manipulation

The clinical application furthest along is retinitis pigmentosa, a severe eye disease in which light-sensitive cells progressively deteriorate. Multiple clinical studies are underway introducing channelrhodopsin into patients' cells and pairing the technique with a device to restore vision. If this proves a breakthrough, applications to psychiatric conditions such as depression come into view. Deisseroth, as a practicing psychiatrist, has consistently named alleviating patient suffering as a primary motivation for his research.

Ethical risks also entered the conversation. In experiments by Okuyama Teruhiro (奥山照弘) at the University of Tokyo, mice that had developed aversion toward an aggressor after repeated attacks had the brain circuit associated with that aversion weakened through optogenetics—and the emotion was erased. After the light-based manipulation, the mice no longer avoided their attacker. Suda warned that "there is a real possibility of manipulating emotions and even who a person likes or dislikes," and raised concerns about "light lobotomy"-style misuse and treatments that would erase, say, a patient's aversion to an abusive family member while ignoring the underlying problem entirely. She stressed that researchers themselves must maintain strong ethical awareness and engage in continuous, open discussion.