Most of us know from experience that stress seems contagious; being around stressed people often causes us to feel the same way. But are our brains also affected? If so, how? New research investigates.

It is a fact that stress can leave lasting marks on the brain. For example, studies have shown that those with post-traumatic stress disorder (PTSD) lose volume in their hippocampus, or the brain area responsible for learning and creating new memories.

Additionally, we know from anecdotal evidence and personal experience that stress can be "transferred."

For instance, the partners and relatives of traumatized soldiers reportedly also experience symptoms of PTSD, despite never having been on a battlefield.

Furthermore, a study showed that simply observing fear in others can rewire the brain.

So, does simply being around stressed people cause our brains to change as well? Researchers at the University of Calgary in Alberta, Canada, set out to investigate.

The team was led by senior author Jaideep Bains, PhD, and the findings were published in the journal Nature Neuroscience.

Brain changes 'identical' between partners

Bains and colleagues examined the effects of stress on the brains of male and female mice, which were paired together. The researchers took one mouse from each pair, subjected them to a mild level of stress, and then returned them to their partner.

Then, they examined the behavior of a certain group of neurons in the hippocampus. The research showed that the neuronal circuits of both the mice that had been stressed and the ones that had just observed stress in their partner changed in the same way.

"The neurons that control the brain's response to stress showed changes in unstressed partners that were identical to those we measured in the stressed mice," says first study author Toni-Lee Sterley.

Additionally, the researchers found that the activation of this group of neurons caused the animals to release a chemical that they referred to as an "alarm pheromone." The study authors speculate that the purpose of such a signal could be that once alerted, the partner can also alert the other members of their group.

"The study also demonstrates that traits we think of as uniquely human are evolutionary conserved biological traits," says Bains.

Sterley also chimes in, saying, "There has been other literature that shows stress can be transferred—and our study is actually showing the brain is changed by that transferred stress."

Social interaction may erase effects

Finally, the last remarkable discovery of the study was that female mice who had been stressed by contagion were able to have their brain changes reversed by simply spending more time with an unstressed partner.

However, males did not benefit from being around an unstressed female partner.

"If some of the effects of stress are erased through social interactions, but this benefit is limited to females, this may provide insights into how we design personalized approaches for the treatment of stress disorders in people."

Jaideep Bains, PhD

"What we can begin to think about is whether other people's experiences or stresses may be changing us in a way that we don't fully understand," he adds.