Male-female pairs of mice show resilience in coordinating fear responses

When faced with a potential threat, mice often freeze in place. Moreover, when two animals are together, they typically freeze at the same time, matching each other's periods of immobility. 

In a new study, researchers found that coordination during fear looks different in males and females - and changes when stress is involved. 

Male-female mouse pairs consistently stayed in sync during stressful situations, even when the animals were strangers. Same-sex pairs were more likely to fall out of step. 

The findings, published in Biological Psychiatry Global Open Science, suggest that opposite-sex pairs may rely on a more flexible or complex coordination strategy - one that doesn't break down under emotional pressure.

Opposite-sex pairs showed a surprising resilience. They synchronized their fear responses regardless of emotional context. And unlike same-sex pairs, they didn't seem to rely on one clear strategy to do it."

Alexei Morozov, assistant professor at the Fralin Biomedical Research Institute at VTC and corresponding author of the study

Although the research was conducted in mice, the study may offer clues about how sex and emotional context shape social behavior in other species, including people. 

Experts say the findings may shed light on the brain mechanisms involved in conditions like anxiety and post-traumatic stress disorder.

"This clever and well-designed study offers a new way to measure how animals synchronize their fear responses - and shows that males and females do it differently," said Vadim Bolshakov, a professor of psychiatry at Harvard Medical School and at McLean Hospital, who was not involved in the research. "It highlights the complex interaction between social and emotional signals in stressful moments. The reported findings are unique and could potentially help inform strategies to support people who struggle with fear and stress regulation."

In the study, mice learned to associate a sound with a mild but unpleasant stimulus. Later, when they heard the tone again, they froze. By observing how pairs of mice froze and moved together, the researchers were able to measure how closely their behaviors aligned.

Same-sex pairs showed distinct coordination styles. Males tended to copy each other's actions - when one froze or moved, the other followed. 

Females behaved differently, becoming more responsive to their partners. If they initiated an action and their partner didn't respond in the same way, they often stopped and corrected their own behavior. 

"Males copy. Females self-correct," Morozov said. "Both strategies can get you to the same place - synchronization - but they're built on different kinds of social processing. If you have male and female together, somehow, they form a strong social unit against stress." 

Mixed-sex pairs remained unaffected by stress and continued to synchronize at a high level, regardless of familiarity.

Research Assistant Professor Wataru Ito was the first author of the study, which included Andrew Holmes of the Laboratory of Behavioral and Genomic Neuroscience of the National Institute on Alcohol Abuse and Alcoholism.

The study was supported by the National Institute of Mental Health of the National Institutes of Health and the Fralin Biomedical Research Institute's Seale Innovation Fund.