For centuries, philosophers have asked: where, in the mind, does a decision begin? Is there a moment we can point to and say—there, that’s when the mind… made up its mind?

Neuroscience has long tried to answer this question by peering into tiny corners of the brain, studying a handful of neurons at a time. But now, in an unprecedented act of scientific coordination, researchers have created the first full map of brain-wide activity during decision-making—one that captures nearly the entire theater of thought.

The result is a dazzling snapshot of the brain in motion. “The decision-making activity, and particularly reward, lit up the brain like a Christmas tree,” said Alexandre Pouget, a computational neuroscientist at the University of Geneva and co-founder of the International Brain Laboratory (IBL).

A Steering Wheel, a Mouse, and a Global Effort

The breakthrough came from a lab collective. The International Brain Laboratory, or IBL, brought together 22 labs across Europe and the U.S. Each lab trained mice to play a deceptively simple video game: move a striped circle toward the center of a screen using a tiny LEGO steering wheel. The quicker and more accurate the move, the sweeter the sip of sugar water they’d earn.

But here’s the twist. Sometimes the target on the screen was so faint it was barely visible. To succeed, the mice had to fall back on experience—on prior expectations about where the target would appear.

That made the task ideal for studying one of the brain’s most elusive skills: how we use both current sensory information and past experience to make decisions.

And while each lab focused on different brain regions, they all followed the same rigorous protocols. The result is a dataset of staggering scope: more than 620,000 neurons recorded from 139 mice across 279 brain regions.

“This had never been done before,” said Alejandro Pan Vazquez, a research scholar at Princeton University.

The Brain is a Democracy, Not a Dictatorship

What the scientists found upended traditional views of how decisions are made.

For decades, researchers believed that specific brain areas acted as decision hubs. But the new data showed something different. “If there’s one thing we’ve discovered from this work,” Pouget told New Scientist, “it’s that no one brain area ‘decides’. Decision making involves tens of areas that decide through a kind of consensus.”

This distributed process starts before the decision is even made. Neural signals associated with upcoming choices begin building before any movement occurs. In some cases, those signals were detectable even before the stimulus appeared on screen.

And these weren’t just found in the frontal cortex or parietal lobe—the usual suspects in cognition. The signals rippled across regions involved in movement, vision, reward, and even the hindbrain and cerebellum.

“One of the important conclusions of this work is that decision-making is indeed very broadly distributed throughout the brain, including in regions that we formerly thought were not involved,” said Ilana Witten, a neuroscientist at Princeton.

That includes deep brainstem areas like the gigantocellular reticular nucleus, which showed especially strong signals tied to the mice’s choices.

What About Intuition?

The second of two Nature papers released by the IBL focused on expectation, or the brain’s ability to guess what will happen next based on past experiences. Here too, the signals were everywhere.

Some appeared shockingly early in the process, even as sensory information was leaving the eye and traveling to the thalamus. That’s before any conscious awareness of the stimulus.

“This might correspond with what we perceive as intuition,” said Pouget. The brain, in this view, is constantly predicting. In other words, the brain is not passively receiving information but actively shaping what we perceive based on what it expects to find.

“This suggests that it is our own behavior and subjective experience that shapes what we expect to see next, rather than the true, objective state of the world,” added Laurence Hunt, a neuroscientist at the University of Oxford, as per New Scientist.

A Model for Big Neuroscience

The science alone would have made headlines. But perhaps just as striking is the way it was done.

In a field infamous for small sample sizes and fragmented findings, IBL set out to show what a coordinated, reproducible neuroscience experiment could look like. Labs used the same behavior protocols, shared the same analysis pipelines, and even sent brain samples to a centralized histology lab at University College London.

“The brain is the most complex structure we know of in the universe,” said Tom Mrsic-Flogel, director of the Sainsbury Wellcome Centre in London. “Understanding how it drives behavior requires international collaboration on a scale that matches that complexity.”

The result is more than a study—it’s a benchmark. A resource. And a proof of concept.

“All data from these studies, along with detailed specifications of the tools and protocols used for data collection, are openly accessible to the neuroscience community for further analysis and research,” said Anne Churchland of UCLA.

What’s Next?

While the project focused on a single decision-making task, the researchers plan to expand their approach. Future studies may explore how the brain navigates memory, attention, or even mental illness.

Already, the findings could inform research into conditions like autism and schizophrenia, where disruptions in expectation and prediction may play a role. “Mouse models of autism suggest these animals have difficulties updating their prior expectations,” said Pouget, “which fits with what we see behaviorally in people.”

More broadly, the IBL hopes to bring more scientists into its orbit. “[This] marks a beginning, not the grand finale,” said Tatiana Engel, a neuroscientist at Princeton. “The IBL has set the highest standards for sharing high-quality data, tools, and resources to accelerate scientific progress. Now, the next horizon is to extend this collective expertise to the entire community.”

The brain, it turns out, doesn’t make decisions in isolation—and neither should science.

The findings are detailed in two companion papers published in Nature on September 3, 2025: “A brain-wide map of neural activity during complex behaviour” and “Brain-wide representations of prior information.”