The implications extend beyond mice. Human brains, though far larger and more complex, share a similar architecture. Understanding how decisions emerge from the distributed chatter of cells could eventually illuminate disorders where this chatter goes awry, such as schizophrenia or Parkinson's.
Until now, studies of decision-making have tended to focus on small clusters of cells within single regions of the brain. The new study shows how limiting that approach has been.
A decision, it turns out, is not hatched in a single cortical enclave, but emerges from a grand orchestration of regions spread across the brain, including those once understood to be the preserve of movement rather than thought.
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At first the mouse's brain is relatively silent. As the circle appears on the screen, visual areas at the back of the brain stir into action.
Activity then swells across several regions as the animal accumulates evidence about what it sees. As a choice crystallises, areas linked to movement ignite and the mouse pushes the wheel to play its computer game. When the sugar water reward arrives, the whole brain lights up in a final surge of activity.
What is most striking, according to researchers, is how the activity is spread out. "Decision-making is indeed very broadly distributed throughout the brain, including in regions that we formerly thought were not involved," said Ilana Witten, a professor at the Princeton Neuroscience Institute and one of the project's leaders.
This brain-wide activity means that neuroscientists will need to take a broader approach when studying complex behaviour.
The results also suggest that expectations shaped by recent experience are stored all over the brain, not just in one spot. Surprisingly, these expectations are not only found in areas associated with thought, but also areas of the brain that process sensory information and control movement.
Technically, the undertaking was formidable. Each of the 22 laboratories was assigned a portion of the brain to monitor with high-density electrodes and the scale of collaboration marks its own breakthrough.
Professor Tom Mrsic-Flogel, the director of the Sainsbury Wellcome Centre at University College London and one of the core members of the International Brain Laboratory, said: "We'd seen how successful large-scale collaborations in physics had been at tackling questions no single lab could answer, and we wanted to try that same approach in neuroscience.
"The brain is the most complex structure we know of in the universe and understanding how it drives behaviour requires international collaboration on a scale that matches that complexity."
The mice's task was, by contrast, relatively simple. They sat before a screen where circles flashed briefly to the left or right. By twiddling the wheel, they could pull the circle to the centre and win a sip of sugar water. Sometimes the circle was faint, forcing the animals to rely on memory and expectation -- a way of testing how recent experience influences decision-making.
The resulting data, now public, will offer a benchmark against which theories can be tested and refined.