The mouse hesitates for a beat. A tiny steering wheel sits in front of it, circles glowing on a nearby screen. A flick to the left or the right could mean sweet reward — or nothing at all. At that exact instant of uncertainty, hundreds of thousands of neurons across its brain begin to fire in a coordinated storm.
For the first time, scientists have captured that storm in full. In a landmark project spanning 12 laboratories and more than a hundred animals, researchers mapped brain activity during decisionmaking across 95 percent of the mouse brain. The feat is being hailed as a milestone — not just for the technology that made it possible, but for what it reveals about the very nature of thought.
No Single “Control Room”
The dream of neuroscience has long been to find the seat of decisionmaking: a distinct cluster of cells issuing commands, like executives around a boardroom table. This new map suggests that model was far too simple.
When the mice weighed their choices, activity didn’t stay confined to one zone. Instead, neurons across 279 regions lit up. Signals bounced between motor circuits, sensory areas, and deeper processing hubs, revealing decisionmaking as a distributed, network-wide process.
“It’s not a single region giving orders,” said Daniel Birman, a neuroscientist with the International Brain Laboratory. “It’s a conversation happening everywhere at once.”
A Technical Breakthrough
The project relied on electrodes implanted in the brains of 139 mice, recording activity from more than 620,000 neurons. Of those, about 75,000 were cleanly isolated and analyzed in detail — a number that dwarfs anything achieved in previous studies.
Until now, whole-brain maps of decisionmaking were limited to small animals like fruit flies or fish larvae. In mammals, only fragments of brain tissue had been studied at once. The resolution of this dataset — spanning both the scale and complexity of a rodent brain — marks a leap toward bridging that gap.
Training for Choice
To trigger real decisions, researchers trained the mice to manipulate a steering wheel. If the animals moved shapes on the screen toward the center, they earned a sip of sugar water. Success required interpreting sensory cues, weighing options, and executing a physical response — a process mirroring, in miniature, the fundamental steps of decisionmaking across species.
By pairing this behavioral task with continuous recordings, the team could watch thought cascade across the brain from perception to action.
A Public Map of the Thinking Brain
The dataset — now open access — is already drawing attention. Neuroscientists say it provides the most detailed view yet of how the brain integrates information when confronted with choice.
“It’s like watching the final scene of a movie we’d only guessed at,” said Juan Lerma, a researcher at Spain’s National Research Council, who was not involved in the study. “We suspected the ending, but now we can actually see it.”
The findings, published in Nature, confirm that decisionmaking taps into more regions than expected, while sensory processing remains more localized.
