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Mild traumatic brain injury affects fear processing, post-deployment PTSD risk

PHILADELPHIA — Experiencing mild traumatic brain injury before and during deployment was associated with changes in acquisition and retention of conditioned fear, and somewhat accounted for variance in the association between mild traumatic brain injury and post-deployment PTSD symptoms.

“Mild traumatic brain injury increases risk for developing PTSD, but the mechanisms through which [mild traumatic brain injury] produce increased risk are unclear. One potential mechanism is via alteration of learned fear processes which could affect conditioned responses to trauma memories and cues,” Daniel Glenn, PhD, of the Center of Excellence for Stress and Mental Health, San Diego Veterans Affairs Health Services, and colleagues wrote.

To examine associations between mild traumatic brain injury, learned fear responses and extinction and PTSD risk, researchers assessed 852 individuals serving in the U.S. Marines or Navy in Afghanistan. Study participants completed assessments of mild traumatic brain injury history and PTSD symptoms before and after deployment. They also completed a fear conditioning and extinction paradigm postdeployment.

Individuals who experienced mild traumatic brain injury both before and after deployment exhibited increased learned fear during acquisition and extinction and poorer retention of safety learning, compared with individuals with one or fewer mild traumatic brain injury events.

Experiencing mild traumatic brain injury during deployment was associated with increased change in PTSD, depression and anxiety scores.

Fear learning processes did not mediate the relationship between mild traumatic brain injury during deployment and change in PTSD symptoms. However, researchers found evidence of moderated mediation. The interaction between mild traumatic brain injury before and during deployment was necessary for mediation.

Findings did not indicate mediation or moderated mediation of associations between mild traumatic brain injury and changes in depression or anxiety scores.

“These results suggest that experiencing a ‘double hit’ of both recent predeployment [mild traumatic brain injury] and deployment [mild traumatic brain injury] is associated with altered acquisition and retention of conditioned fear,” the researchers wrote. “Further, this association accounts for some variance in the relationship between [mild traumatic brain injury] and post-deployment PTSD symptoms. Repeated [mild traumatic brain injury] within a 2.5-year time frame may alter neural circuitry underlying fear learning, thereby conferring increased psychiatric risk for fear disorders.” – by Amanda Oldt

Reference:

Glenn D, et al. Traumatic brain injury during combat deployment alters fear conditioning processes: A potential mechanism for TBI association with PTSD symptoms. Presented at: Anxiety and Depression Association of America Conference; March 31-April 3, 2016; Philadelphia.

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