Neuroscientists explore how the brain makes decisions

Scientists have gained new insights into how neurons in the brain communicate when making a decision and how connections between neurons can help reinforce a choice.

The study, conducted in mice and led by neuroscientists at Harvard Medical School, is the first to combine structural, functional and behavioral analyzes to explore how neuron-to-neuron connections support decision-making.

The results are published in the journal Nature.

“How the brain is organized to help make decisions is a fundamental and important question, and the neural circuits (how neurons are connected to each other) in brain areas important for decision making are not well understood. understood,” said Wei-Chung Allen Lee, associate professor of neurobiology at the Blavatnik Institute at HMS and professor of neurology at Boston Children’s Hospital.

Lee is co-senior author of the paper with Christopher Harvey, professor of neurobiology at HMS, and Stefano Panzeri, professor at University Medical Center Hamburg-Eppendorf.

In the research, mice were tasked with choosing which path to take in a maze to find a reward. The researchers found that a mouse’s decision to go left or right activated sequential groups of neurons, resulting in the suppression of neurons related to the opposite choice.

These specific connections between groups of neurons can help make decisions by closing neural pathways for alternative options, Lee said.

A fruitful collaboration is born

It was a chance meeting on a bench outside their building during a fire drill that led Harvey and Lee to realize how complementary their work was. That day, they struck up a collaboration that propelled the new work.

The Harvey lab uses mice to study behavioral and functional aspects of decision making. Typical experiments involve placing a mouse in a virtual reality maze and recording neural activity as it makes decisions. Such experiments have shown that distinct, but intertwined, sets of neurons fire when an animal chooses left or right.

Lee works in a new field of neuroscience called connectomics, which aims to comprehensively map the connections between neurons in the brain. The goal, he says, is to determine “which neurons communicate with each other and how the neurons are organized into networks.”

By combining their expertise, Harvey and Lee were able to delve deeper into the different types of neurons involved in decision-making and how these neurons are connected.

Choose a direction

The new study focused on a region of the brain called the posterior parietal cortex, what Lee describes as an “integration center” that receives and processes information gathered by multiple senses to help animals make decisions.

“We wanted to understand how neural dynamics arise in this area of ​​the brain important for navigation decision-making,” Lee said. “We are looking for connectivity rules, simple principles that form the basis of the brain’s calculations when making decisions.”

The Harvey lab recorded neural activity as mice ran a T-shaped maze in virtual reality. A signal, occurring several seconds before, told the mice whether a reward would be in the left or right arm of the T. Lee’s lab used powerful microscopes to map the structural connections between the same neurons recorded during the maze task.

By combining the modalities, the researchers distinguished excitatory neurons, those which activate other cells, from inhibitory neurons, which suppress other cells. They discovered that a specific set of excitatory neurons fired when a mouse decided to turn right, and that these “right-turning” neurons activated a set of inhibitory neurons that dampened the activity of the “left-turning” neurons. . The opposite happened when a mouse decided to turn left.

“As the animal expresses a choice, the wiring of the neural circuit can help stabilize that choice by suppressing other choices,” Lee said. “This could be a mechanism that helps an animal maintain a decision and prevents ‘changes of mind’.”

The results need to be confirmed in humans, although Lee expects some conservation between species.

The researchers see many directions for future research. One of them explores the connections between neurons involved in decision-making in other regions of the brain.

“We used these combined experimental techniques to find one connectivity rule, and now we want to find more,” Lee said.