Scientists can now rewire living brains

Scientific American · Simon Makin · 2026-10-29 11:30 UTC

The tool could eventually lead to an entirely new approach for treating mental health

The human brain holds around 86 billion neurons, wired together in a vast web of hundreds of trillions of connections. These connections, bridged by structures called synapses, form circuits responsible for everything we feel, perceive and do. And they constantly shift as we grow, learn, make memories and form habits.

Neuroscientists have long sought to hack into these circuits to understand how the brain works. Just 20 years ago they developed a technique called optogenetics, which offered some of the first glimpses of these circuits in action—it uses light to turn cells, including brain cells, on and off.

The work won three scientists the 2026 Nobel Prize in Physiology or Medicine. If brain pathways were highways, optogenetics would be akin to “controlling the volume of traffic on a road network that’s already built,” says Sangkyu Lee, a neurobiologist at the Institute for Basic Science in South Korea.

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