Abstract
Evidence suggests a link between smaller hippocampal volume (HV) and post-traumatic stress disorder (PTSD). However, there has been little prospective research testing this question directly and it remains unclear whether smaller HV confers risk or is a consequence of traumatization and PTSD. U.S. soldiers (N = 107) completed a battery of clinical assessments, including structural magnetic resonance imaging pre-deployment. Once deployed they completed monthly assessments of traumatic-stressors and symptoms. We hypothesized that smaller HV would potentiate the effects of traumatic stressors on PTSD symptoms in theater. Analyses evaluated whether total HV, lateral (right v. left) HV, or HV asymmetry (right - left) moderated the effects of stressor-exposure during deployment on PTSD symptoms. Findings revealed no interaction between total HV and average monthly traumatic-stressors on PTSD symptoms b = -0.028, p = 0.681 [95% confidence interval (CI) -0.167 to 0.100]. However, in the context of greater exposure to average monthly traumatic stressors, greater right HV was associated with fewer PTSD symptoms b = -0.467, p = 0.023 (95% CI -0.786 to -0.013), whereas greater left HV was unexpectedly associated with greater PTSD symptoms b = 0.435, p = 0.024 (95% CI 0.028-0.715). Our findings highlight the importance of considering the complex role of HV, in particular HV asymmetry, in predicting the emergence of PTSD symptoms in response to war-zone trauma.
Highlights
The hippocampus is a primary brain region implicated in neurobiological models of post-traumatic stress disorder (PTSD) (Pitman et al, 2012), and there is extensive evidence for smaller hippocampal volume (HV) in posttraumatic stress disorder (PTSD) (Karl et al, 2006; Logue et al, 2018; O’Doherty, Chitty, Saddiqui, Bennett, & Lagopoulos, 2015; Smith, 2005; Woon, Sood, & Hedges, 2010)
Findings revealed no direct effects of pre-deployment HV on in-theater PTSD symptoms across HV indices, including for total HV [b = −0.20, p = 0.071], left HV [b = −0.03, p = 0.872], right HV [b = −0.18, p = 0.460], and right – left HV asymmetry [b = −0.08, p = 0.460]
Total HV did not moderate the effects of within-person deviation from the average number of traumatic stressors [b = −0.025, p = 0.858], nor the average exposure to traumatic stressors on PTSD symptoms [b = −0.028, p = 0.681]
Summary
The hippocampus is a primary brain region implicated in neurobiological models of post-traumatic stress disorder (PTSD) (Pitman et al, 2012), and there is extensive evidence for smaller hippocampal volume (HV) in PTSD (Karl et al, 2006; Logue et al, 2018; O’Doherty, Chitty, Saddiqui, Bennett, & Lagopoulos, 2015; Smith, 2005; Woon, Sood, & Hedges, 2010). Smaller HV was not shown to predict the later emergence of PTSD symptoms, whereas decreases in HV were associated with PTSD symptoms at follow-up This suggests that instead of smaller HV reflecting pre-trauma susceptibility, reductions in HV may reflect the sequela of trauma or development of PTSD. This conclusion is consistent with the hypothesized contribution of stress-evoked hippocampal atrophy to stress-related psychopathology (Sapolsky, 2000), and prior cross-sectional findings of reduced HV in individuals with PTSD (O’Doherty et al, 2015; Woon et al, 2010). U.S soldiers (N = 107) completed a battery of clinical assessments, including structural magnetic resonance imaging pre-deployment Once deployed they completed monthly assessments of traumatic-stressors and symptoms. Our findings highlight the importance of considering the complex role of HV, in particular HV asymmetry, in predicting the emergence of PTSD symptoms in response to war-zone trauma
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