Brain scans of soldiers show people with post-traumatic stress disorder (PTSD) can start to generalize their fear, turning everyday moments into triggers.
Says Rajendra A. Morey, associate professor in the psychiatry and behavioral sciences department at Duke University:
“We know that PTSD patients tend to generalize their fear in response to cues that merely resemble the feared object but are still distinct from it.
This generalization process leads to a proliferation of symptoms over time as patients generalize to a variety of new triggers. Our research maps this in the brain, identifying the regions of the brain involved with these behavioral changes.”
For the study, researchers enrolled 67 military veterans who had been deployed to conflict zones in Iraq or Afghanistan after Sept. 11, 2001, and who had been involved in traumatic events. Thirty-two were diagnosed with PTSD and 35 did not have the disorder.
Heightened Brain Activity
All patients were shown a series of five facial images, depicting a range of emotions from neutral to frightened, while being scanned with functional MRI. The scans showed no dissimilarities between those with PTSD and those unaffected.
Outside the MRI, the participants were shown the images again and given a mild electrical shock when viewing the middle image— the face showing moderate fear.
The patients then underwent another MRI scan as they viewed all five faces. People with PTSD showed heightened brain activity when they saw the most fearful face and associated it with the electric shock, even though they had actually experienced shocks when the middle, less fearful face appeared.
Brain activity was heightened for the non-PTSD group when participants saw the correctly associated middle face.
Triggers That Remind
“The PTSD patients remembered incorrectly and generalized their anxiety to the image showing the most fearful expression,” Morey says. “This phenomenon was captured in MRI scans, showing where the PTSD group had heightened activity.
“The amygdala, which is an important region in responding to threat, did not show a bias in activation to any particular face,” Morey adds. “But there was a definite bias of heightened activity in response to the most frightened expression in brain regions such as the fusiform gyrus, insula, primary visual cortex, locus coeruleus and thalamus.”
The visual cortex is significant because it is not only doing visual processing, but also assessing threats. The locus coeruleus is responsible for triggering the release of adrenaline during stress or serious threat.
These functional brain differences provide a neurobiological model for fear generalization in which PTSD symptoms are triggered by things that merely resemble the source of original trauma.
“People with post-traumatic stress disorder grow anxious based on reminders of past trauma, and generalize that fear to a variety of triggers that resemble the initial trauma,” Morey says.
“Current fear conditioning therapies are limited by repeated use of the same cue to trigger the initial trauma, but they might be enhanced by including cues that resemble, but are not identical to, cues in the original trauma.”
R A Morey, et al. Fear learning circuitry is biased toward generalization of fear associations in posttraumatic stress disorder Translational Psychiatry (2015) 5, e700; doi:10.1038/tp.2015.196
Image: Army Medicine/Flickr