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Brain responses to fear differ in individuals with PTSD, trauma exposure

Functional MRI analysis indicated veterans with PTSD exhibited fear generalization biased to higher emotional stimuli than the original conditioned fear stimulus.

“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,” Rajendra A. Morey, MD, of Duke University, said in a press release. “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.”

To assess generalization of conditioned fear on fear processing neurocircuitry, researchers conducted functional MRI analysis among 32 military veterans with PTSD and 35 with trauma exposure during fear conditioning. Neutral to fearful stimuli were presented prior to conditioning to determine baseline responses, and then after conditioning to assess changes in neural activity.

Participants with PTSD exhibited greater memory distortion of the stimulus, expressing the highest fear intensity towards the stimulus, compared with participants with trauma exposure.

Participants with PTSD had biased neural activation toward high-intensity stimuli in the fusiform gyrus (P < .02), insula (P < .001), primary visual cortex (P < .05), locus coeruleus (P < .04), thalamus (P < .01), and at the trend-level in inferior frontal gyrus (P = .07).

All regions except the fusiform were affected by childhood trauma.

Functional connectivity in the amygdala calcarine (P = .01) and amygdala thalamus (P = .06) selectively increased among participants with PTSD viewing high-intensity stimuli after conditioning.

Conversely, connectivity in the amygdala ventromedial prefrontal cortex selectively increased among participants with trauma exposure (P = .04) compared with those with PTSD during low-intensity stimuli after conditioning.

“People with PTSD grow anxious based on reminders of past trauma, and generalize that fear to a variety of triggers that resemble the initial trauma,” Morey said in the release. “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.” – by Amanda Oldt

Disclosure: The researchers report no relevant financial disclosures.