Amygdala Response Pattern Marks Vulnerability to PTSD


A marker that predicts susceptibility to post-traumatic stress disorder has been discovered by researchers. One area of the brain seems to be more active in people with PTSD when they see surprised or neutral facial expressions, the study found.

It may be essential to recognize one’s susceptibility to developing PTSD. If you knew you were at risk, you might avoid jobs with high stress and potential trauma or seek treatment as soon as you experienced a potentially triggering event.

Post-traumatic stress disorder is defined by a number of symptoms, but the researchers were particularly interested in hypervigilance — the constant feeling that you need to monitor your environment for potential threats, according to Cecilia Hinojosa, first author of the study and now a postdoctoral researcher at Emory University focusing on PTSD in women.

Hypervigilance in Emotional Ambiguity

Previous research had discovered that hypervigilance can cause people with PTSD to react fearfully to signals that are ambiguous or not clearly threatening — for example, hearing a firecracker may trigger fears of gunshots.

The researchers investigated fMRI brain activation studies of male identical twin pairs. The researchers were able to determine which traits are familial and which are not by studying identical twins who share the same genes.

In a group of 12 identical twin pairs, one twin had been exposed to trauma and developed PTSD, while the other had not. As a control group, 15 identical twin pairs were used. One of the twins had been exposed to trauma but had not developed PTSD, while the other had not.

While people with PTSD have been studied for their reactions to trauma-related imagery, no one has previously examined their responses to ambiguous imagery while performing brain activation scans. The study concentrated on two brain mechanisms.

Medial Frontal Gyrus and Amygdala

The first mechanism was increased activation of the amygdala, a part of the brain involved in processing fear-related stimuli and resulting in the fight, flight, or freeze response.

“Every time we experience something that could be potentially threatening in our environment, the amygdala starts a chain of reaction of responses in the brain,”

said Hinojosa, who worked on the study with Lisa Shin, a Tufts professor of psychology and an expert on PTSD.

The second mechanism involves the activation of the medial frontal gyrus, a prefrontal cortex region that inhibits the amygdala’s response to non-threatening stimuli.

A 2021 study by Greg Fonzo at University of Texas at Austin found that there was a reduction in communication between the amygdala and the insula in PTSD patients who had undergone trauma-focused psychotherapy.

Facial Expression Responses

The study aimed to determine whether people have preexisting brain activation patterns that make them more susceptible to PTSD, or whether they acquire these activation patterns as a result of PTSD.

While the researchers anticipated that men with PTSD would exhibit greater amygdala activation when viewing faces with surprised expressions, they did not anticipate the same response to neutral facial expressions. Interestingly, the same was true of the participants’ non-PTSD-afflicted twins who had not been exposed to trauma.

In contrast, the group of trauma survivors who had not been diagnosed with PTSD did not exhibit the same heightened amygdala response to either the surprised or neutral faces. Hinojosa notes that these findings suggest that individuals with greater amygdala activation prior to trauma may be more susceptible to developing PTSD.

Neurotoxic Stress

Hinojosa suggests that if a person has a preexisting susceptibility to developing PTSD, as indicated by heightened amygdala activation, and experiences a traumatic event, we may be able to provide them with treatments as soon as the trauma occurs to hopefully prevent the development of PTSD symptoms.

The study’s final conclusion is that the decreased reactivity in the medial frontal gyrus, which dampens an excessive fear response, was only observed in the group with PTSD. According to Hinojosa, this suggests that the decreased response in the prefrontal cortex is an acquired characteristic of PTSD.

She referenced animal studies that suggest that chronic stress or traumatic events are neurotoxic. Stress and trauma could harm certain brain regions, so they don’t function as well.

Hinojosa added that the study would need to be repeated with larger sample sizes and expanded to include subjects other than men.

  1. Cecilia A. Hinojosa, Michael B. VanElzakker, Katherine C. Hughes, Reid Offringa, Lisa M. Sangermano, Isabella G. Spaulding, Lindsay K. Staples-Bradley, Ethan T. Whitman, Natasha B. Lasko, Scott L. Rauch, Scott P. Orr, Roger K. Pitman, Lisa M. Shin. Exaggerated amygdala activation to ambiguous facial expressions is a familial vulnerability factor for posttraumatic stress disorder. Journal of Psychiatric Research, Volume 156, 2022, Pages 451-459, ISSN 0022-3956