Abstract
BackgroundPTSD is associated with reduction in hippocampal volume and abnormalities in hippocampal function. Hippocampal asymmetry has received less attention, but potentially could indicate lateralised differences in vulnerability to trauma. The P300 event-related potential component reflects the immediate processing of significant environmental stimuli and has generators in several brain regions including the hippocampus. P300 amplitude is generally reduced in people with PTSD.MethodsOur study examined hippocampal volume asymmetry and the relationship between hippocampal asymmetry and P300 amplitude in male monozygotic twins discordant for Vietnam combat exposure. Lateralised hippocampal volume and P300 data were obtained from 70 male participants, of whom 12 had PTSD. We were able to compare (1) combat veterans with current PTSD; (2) their non-combat-exposed co-twins; (3) combat veterans without current PTSD and (4) their non-combat-exposed co-twins.ResultsThere were no significant differences between groups in hippocampal asymmetry. There were no group differences in performance of an auditory oddball target detection task or in P300 amplitude. There was a significant positive correlation between P300 amplitude and the magnitude of hippocampal asymmetry in participants with PTSD.ConclusionsThese findings suggest that greater hippocampal asymmetry in PTSD is associated with a need to allocate more attentional resources when processing significant environmental stimuli.
Highlights
Post Traumatic Stress Disorder (PTSD) is associated with reduction in hippocampal volume and abnormalities in hippocampal function
We found that seven subjects with PTSD had a reversal of normal asymmetry with a larger left than right hippocampus, and five had a normal asymmetry with a larger right hippocampus
We found positive correlations between hippocampal volume asymmetry and P300 amplitude in participants with PTSD at sites Pz (r = .69, n = 12, p ≤ .025) and P3 (r = .64, n = 12, p ≤ .025), with higher magnitudes of hippocampal volume asymmetry associated with larger P300 values (Table 2)
Summary
PTSD is associated with reduction in hippocampal volume and abnormalities in hippocampal function. The P300 event-related potential component reflects the immediate processing of significant environmental stimuli and has generators in several brain regions including the hippocampus. P300 amplitude is generally reduced in people with PTSD. Post Traumatic Stress Disorder (PTSD) is characterised by recurrent and intrusive memories, avoidance, and hyperarousal. PTSD is associated with impairment in attention, and some studies have shown deficits in learning and memory [1] It has been suggested that disturbed processing of new environmental information in PTSD is due to continuous background re-processing of traumatic events, resulting in modifications of neural circuits [2,3]. The hippocampus is part of a large extended network involving the learning of material available within working memory. The HC contributes to regulation of the hypothalamic-pituitaryadrenocortical system, which is crucial in both acute and chronic responses to stress [9]
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