Previous research has found that hypervigilance can lead people with PTSD to respond with fear to cues that are ambiguous or not overtly threatening—for example, hearing fireworks can trigger a fear of gunshots.
A team led by Tufts researchers studied male identical twin pairs using fMRI studies of brain activation. By studying identical twins who share the same genes, researchers have been able to show which traits are familial and which are not.
In 12 identical twin pairs, one twin was traumatized and developed PTSD, while the other was not traumatized. A set of 15 identical twin pairs was used as a control group. One member of this twin set was traumatized but did not develop PTSD, while the other was not.
Although the responses of people with PTSD to trauma-related images have been studied, no one has previously examined their responses to ambiguous images while performing brain activation scans. The research team focused on two brain mechanisms.
Mechanisms of PTSD
The first was increased activation of the amygdala, which is involved in the brain’s processing of fear-related stimuli and results in the fight, flight, or freeze response.
“Every time we encounter something potentially threatening in our environment, the amygdala starts a chain of reactions in the brain,” said Hinojosa, an expert on PTSD who worked on the study with Tufts psychology professor Lisa Shin as a graduate student.
The second mechanism is the activation of the medial frontal gyrus, a part of the prefrontal cortex involved in inhibiting the amygdala’s response to things that are not actually threatening.
The study, which involved researchers from Tufts, MGH, Duke and the National Institutes of Health, sought to find out whether there are brain activation patterns that make people more susceptible to PTSD, or whether they acquire this activation pattern because they have PTSD. .
While the researchers expected men with PTSD to show greater activation of the amygdala when observing faces with surprising gazes, they did not expect the participants to respond similarly to neutral facial expressions. Almost the same was true in participants’ non-traumatized co-twins without PTSD.
On the other hand, the group who had been traumatized but not diagnosed with PTSD did not show the same heightened amygdala response to surprised or neutral faces.
Hinojosa notes that these findings may mean that individuals with greater amygdala activation prior to experiencing trauma may be more susceptible to developing PTSD.
The findings could also mean that if a person is vulnerable to developing PTSD with increased amygdala activation and experiences a traumatic event, “we can potentially provide treatment to them as soon as they experience that trauma to prevent the development of PTSD symptoms.” ,” Hinojosa says.
The conclusion of the study is that the reduction in reactivity in the medial frontal gyrus, which reduces the extreme fear response, occurred only in the PTSD group.
He pointed to studies in nonhuman animals showing that chronic stress or traumatic events are neurotoxic. Stress and trauma “can damage that area of the brain, so it doesn’t work well,” he says.
For next steps, Hinojosa says, the study needs to be replicated with larger sample sizes and go beyond just the male subjects in the current study.