A key to understanding the brain lies in unpacking how hundreds of interconnected brain areas process information that leads to various outputs. In order to try to understand this, researchers investigate both single neurons and groups of neurons together. Now, a major advance in this area of neuroscience study has been published: the first complete activity map of the brain has been unveiled by a large international collaboration of neuroscientists.
Two papers published in Nature reveal insights into how decision-making unfolds across the entire brain in mice at the resolution of single cells. This brain-wide activity map shows that decision-making is distributed across many regions in a highly coordinated way.
“This is the first time anyone has produced a full, brain-wide map of the activity of single neurons during decision-making,” explained Professor Alexandre Pouget, PhD, co-founder of the International Brain Laboratory (IBL) and group leader at the University of Geneva. “The scale is unprecedented as we recorded from over half a million neurons across mice in 12 labs, covering 279 brain areas, which together represent 95% of the mouse brain volume. The decision-making activity, and particularly reward, lit up the brain like a Christmas tree.”
IBL utilized a collaborative model that uses a standardized set of tools and data processing pipelines shared across multiple labs, ensuring data reproducibility. Researchers across 12 labs used state-of-the-art electrodes for simultaneous neural recordings—Neuropixels probes—to measure brain activity while mice were carrying out a decision-making task. In the task, a mouse sits in front of a screen and a light appears on the left or right side. The mouse then responds by moving a small wheel in the appropriate direction to receive a reward. However, in some trials, the light is so faint that the animal must guess which way to turn the wheel. The mouse uses how often the light has appeared on the left or right previously to help them make this guess. These challenging trials therefore allowed the researchers to study how prior expectations influence perception and decision-making.
The first paper, “A brain-wide map of neural activity during complex behavior,” showed that decision-making signals are distributed across the brain, not localized to specific regions. This adds to a growing number of studies that challenge the traditional hierarchical model of brain function and emphasizes that there is constant communication across brain areas during decision-making, movement onset, and even reward.
More specifically, the team reports “a comprehensive set of recordings from 621,733 neurons recorded with 699 Neuropixels probes across 139 mice in 12 laboratories. The probes covered 279 brain areas in the left forebrain and midbrain and the right hindbrain and cerebellum.”
The second paper, “Brain-wide representations of prior information,” showed that prior expectations—beliefs about what is likely to happen based on our recent experience—are encoded throughout the brain. These expectations are not only found in cognitive areas, but also brain areas that process sensory information and control actions. For example, expectations are even encoded in early sensory areas such as the thalamus, the brain’s first relay for visual input from the eye. This supports the view that the brain acts as a prediction machine, but with expectations encoded across multiple brain structures playing a central role in guiding behavior responses. These findings could have implications for understanding conditions such as schizophrenia and autism, which are thought to be caused by differences in the way expectations are updated in the brain.
More specifically, the authors note that “mice were trained to indicate the location of a visual grating stimulus, which appeared on the left or right with a prior probability alternating between 0.2 and 0.8 in blocks of variable length.” Their work suggests that mice “estimate this prior probability and thereby improve their decision accuracy.” Furthermore, they report that this subjective prior is encoded in at least 20% to 30% of brain regions that span all levels of processing, from early sensory areas to motor regions and high-level cortical regions.
“The map describes the activity of over 650,000 individual neurons with single-spike resolution. This activity underlies the brain’s sensory and motor activity that constitutes a decision. The map is a fantastic resource that is already being mined by myriad scientists, and yielding unexpected discoveries. It’s a great success for team science and open science,” commented Matteo Carandini, PhD, professor of Visual Neuroscience at University College London and one of the core members of IBL.
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.
The post In a First, Brain-Wide Activity Mapped During Decision-Making appeared first on GEN – Genetic Engineering and Biotechnology News.
