What if you could control individual neurons in a living brain with a flash of blue light? The idea, now known as optogenetics, seemed absurd just a decade ago. Then Karl Deisseroth made it happen. A profile of the 43-year-old Stanford University psychiatrist in the 18 May issue of The New Yorker details his inspiring journey from dreamer to doyen, with adorable quotes from his neuroscientist-wife, Michelle Monje. “It’s like Beatlemania,” Monje says of her husband’s rock star status at neuroscience meetings. “I realized, I’m married to a Beatle. The nerdy Beatle.” Deisseroth also created CLARITY, a technique that renders postmortem brains transparent to reveal perfectly intact neurons.