How Our Past Trauma Drives Our Brain’s Response to New Stress

A new study published in the Proceedings of the National Academy of Sciences offers insight into how past stress impacts a person’s response to new stress.

There are two leading hypotheses about how trauma drives future responses to stress. One is the sensitization hypothesis, which poses that having a history of stress will make someone more reactive to future stressful situations.

“The thought is they’re primed for stress and hypersensitive,” explains principal investigator Elizabeth Goldfarb, PhD, assistant professor of psychiatry at Yale School of Medicine (YSM).

The other is the habituation hypothesis, which suggests that individuals with past trauma will essentially acclimate to stress and not have as strong of a response when new stress arises. Goldfarb and her colleagues were interested in putting both of these hypotheses to the test.

When it comes to past traumatic events, the brain keeps the score. Various neural networks connect different brain regions and allow them to communicate with each other. Some of these networks are associated with stress.

In the new study, researchers found that when individuals with past trauma were exposed to mild stress, these past trauma-related brain networks showed reduced connectivity, meaning they observed decreased synchronized communication across the associated brain regions.

“We asked what these networks do when you’re faced with a stressful situation,” says Goldfarb. “We found that when you’re in a mildly stressful situation, it’s helpful for your daily functioning and mental health symptoms to turn down that trauma network.”

The researchers collected data from 170 people in the New Haven community, specifically about their lifetime exposure to traumatic events. “This encompasses anything from whether they’ve experienced psychosocial trauma, car accidents, natural disasters, and so on,” explains Felicia Hardi, PhD, postdoctoral fellow at Yale’s Wu Tsai Institute and the study’s first author.

Using functional magnetic resonance imaging data and machine learning, the researchers first identified brain networks associated with past trauma. Then, they tested how these brain networks responded to stress in two experiments. In the first, participants underwent a standard procedure for inducing stress that involves placing an arm in ice water. In a second separate experiment, participants received a pharmacological intervention with hydrocortisone, a hormone that the body releases in response to stress.

“We looked at how the brain keeps a record of past stressful events by identifying networks where stronger connections correspond to having more stressful life events in the past,” explains Goldfarb. “Then, we subjected that network to a mildly stressful situation in real time and tracked how it responded.”

In both experiments, brain networks associated with past trauma had reduced connectivity following mild stress, findings that support the habituation hypothesis.

“We found that individuals were disengaging their trauma network when they were faced with mild stress,” says Hardi.

Furthermore, across all participants, people who experienced fewer depressive symptoms showed a more pronounced decrease in brain network connectivity.

“This suggests individuals with better mental health seem to be habituating their past trauma-related brain network more in the face of current stress,” Hardi adds.

Unpacking the relationship between trauma history and how we experience new stressful situations is an ongoing area of study. This research helps inform the big-picture questions around when stress may be helpful, and how the brain’s adaptive stress responses can be useful in challenging situations later on.

“There are many future directions for this work,” says Hardi.

The research reported in this news article was supported by the National Institutes of Health (awards K01AA027832KL2 and R21MH128740) and Yale University. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. Additional support was provided by the Yale Wu Tsai Institute, the National Center for PTSD, and the Brain and Behavior Research Foundation.