Abstract
Reduced hippocampal volume is frequently observed in posttraumatic stress disorder (PTSD), but the psychological processes associated with these alterations remain unclear. Given hippocampal involvement in memory and contextual representations of threat, we investigated relationships between retrospectively reported combat exposure, perceived threat, and hippocampal volume in trauma-exposed veterans. T1-weighted anatomical MRI scans were obtained from 56 veterans (4 women, 52 men; 39 with elevated PTSD symptoms, “PTSS” group) and hippocampal volume was estimated using automatic segmentation tools in FreeSurfer. Hippocampal volume was regressed on self-reported perceived threat from the Deployment Risk and Resilience Inventory, and combat exposure from the Combat Exposure Scale. As a secondary analysis, hippocampal volume was regressed on Clinician-Administered PTSD Scale (CAPS) symptoms. In veterans with elevated PTSD symptoms, hippocampal volume was inversely related to perceived threat while deployed while controlling for self-reported combat exposure. Hippocampal volume was also inversely correlated with avoidance/numbing CAPS symptoms. Future research should clarify the temporal milieu of these effects and investigate whether individual differences in hippocampal structure and function contribute to heightened threat appraisal at the time of trauma vs. subsequently elevated appraisals of traumatic events.
Highlights
MethodsWe recruited veterans of Operation Enduring Freedom/Operation Iraqi Freedom through community and online advertisements and in collaboration with veterans’ organizations, the Wisconsin National Guard, and the Madison Veterans Affairs Hospital
In combat-exposed veterans with elevated PTSD symptoms, we identified a novel relationship between greater perceived threat while deployed and smaller hippocampal volume measured on average 5 years after deployment, with no such relationships observed for self-reported combat exposure or amygdala volume
These results suggest that the hippocampus is an important neural substrate for individual differences in subjective appraisals of threat, which have previously been shown to influence the development of PTSD and other mood and anxiety disorders
Summary
We recruited veterans of Operation Enduring Freedom/Operation Iraqi Freedom through community and online advertisements and in collaboration with veterans’ organizations, the Wisconsin National Guard, and the Madison Veterans Affairs Hospital. All experimental procedures were approved by the University of Wisconsin-Madison Health Sciences IRB and methods were carried out in accordance with all relevant guidelines and regulations. A team of clinically trained interviewers administered the Clinician-Administered PTSD Scale for DSM-IV (CAPS)[23] and Structured Clinical Interview for DSM-IV (SCID)[24] with supervision from a licensed clinical psychologist (JBN). Exclusionary conditions included substance dependence within the past 3 months and lifetime bipolar, psychotic, or cognitive disorders
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