Understanding how the brain tracks social status and competition

Studies in mice are helping scientists decipher the brain activity involved in social hierarchies and group dynamics. Rost9 / Shutterstock

Most social species, including humans, naturally sort themselves into hierarchies when in a group. An individual’s ranking in these hierarchies can affect their behavior. Researchers are just beginning to understand how the brain responds to and helps drive complex group dynamics, including competition, dominance, and social norms.

In two new NIH-funded studies, researchers explored how the brain tracks social status and whether that predicts how well mice competed for resources. The results were published on March 16, 2022, in Nature.

In one study, a team led by Dr. Kay Tye, a Howard Hughes Medical Institute investigator at the Salk Institute, looked at the brain activity of mice as they competed to drink a sweet liquid. The team housed mice together until a social order emerged. Then, researchers trained each mouse alone that the liquid would appear in the cage after a sound played. Next, the researchers tracked the brain activity of the mice as they competed two at a time to drink the liquid after it appeared. Dominant mice generally drank more liquid than subordinate mice.

The researchers found that the activity of neurons in a part of the brain called the medial prefrontal cortex (mPFC) differed during competition based on the social rank of the opposing mouse. Brain activity in the mPFC could predict a mouse’s social ranking with 90% certainty. These brain patterns could also predict which mouse would win before the competition began. Although the dominant mice were usually the predicted winners, they weren’t always. This indicates that other factors, such as motivation and confidence, also played a role.

Further work found that information about social competition was routed from the mPFC to another area of the brain called the lateral hypothalamus. This region plays a role in many social behaviors. A group of cells connecting the two brain regions showed more activity when mice were drinking the liquid during a competition than when they were alone.

In the other study, a team led by Dr. Ziv Williams from Massachusetts General Hospital tracked mice that were competitively foraging for food. The team used wireless recording devices that could pick up signals from single neurons in the brain.

They found that the activity of individual neurons in a brain region connected to the mPFC, called the anterior cingulate cortex (ACC), changed relative to the social rank of the competitor mice.

ACC activity increased when an animal was the more socially dominant one in the competition and decreased when it was not. How successfully animals foraged for food depended on their rank compared with their competitor. The more dominant ones were usually more successful.

ACC neuron activity also changed depending on whether the mouse had competed successfully in the past. This suggests that the cells play a role in making decisions when the mice encounter similar scenarios.

When the researchers used drugs to manipulate the activity of these neurons, they could influence how hard the mice would compete. But this competitive drive was still influenced by the social rank of the other mice searching for food.

“Collectively, these neurons held remarkably detailed representations of the group’s behavior and their dynamics as the animals competed together for food, in addition to information about the resources available and the outcome of their past interactions,” Williams explains. “Together, these neurons could even predict the animal’s own future success well before competition onset, meaning that they likely drove the animals’ competitive behavior based on whom they interacted with.”

“Most social species organize themselves into hierarchies that guide each individual’s behavior,” Tye says. “Understanding how the brain mediates this may help us understand the interplay between social rank, isolation, and psychiatric diseases, such as depression, anxiety, or even substance abuse.”

—by Sharon Reynolds