Abstract
Background
Two decades of human neuroimaging research have associated volume reductions
in the hippocampus with posttraumatic stress disorder. However, little is
known about the distribution of volume loss across hippocampal subfields.
Recent advances in neuroimaging methods have made it possible to accurately
delineate 10 gray matter hippocampal subfields. Here, we apply a volumetric
analysis of hippocampal subfields to data from a group of combat-exposed
Veterans.
Method
Veterans (total, n = 68, posttraumatic stress disorder, n = 36; combat
control, n = 32) completed high-resolution structural magnetic resonance
imaging. Based on previously validated methods, hippocampal subfield volume
measurements were conducted using FreeSurfer 6.0. The Clinician-Administered
PTSD Scale assessed posttraumatic stress disorder symptom severity; Beck
Depression Inventory assessed depressive symptom severity. Controlling for
age and intracranial volume, partial correlation analysis examined the
relationship between hippocampal subfields and symptom severity. Correction
for multiple comparisons was performed using false discovery rate. Gender,
intelligence, combat severity, comorbid anxiety, alcohol/substance use
disorder, and medication status were investigated as potential
confounds.
Results
In the whole sample, total hippocampal volume
negatively correlated with Clinician-Administered PTSD Scale and Beck Depression Inventory scores. Of the 10
hippocampal subfields, Clinician-Administered PTSD Scale symptom severity
negatively correlated with the hippocampus–amygdala
transition area (HATA). Beck Depression Inventory scores
negatively correlated with dentate gyrus, cornu ammonis 4 (CA4), HATA,
CA2/3, molecular layer, and CA1. Follow-up analysis limited to the
posttraumatic stress disorder group showed a negative correlation between
Clinician-Administered PTSD Scale symptom severity and each of HATA, CA2/3,
molecular layer, and CA4.
Conclusion
This study provides the first evidence relating posttraumatic stress disorder
and depression symptoms to abnormalities in the HATA, an anterior
hippocampal region highly connected to prefrontal-amygdala circuitry.
Notably, dentate gyrus abnormalities were associated with depression
severity but not posttraumatic stress disorder symptoms. Future confirmatory
studies should determine the extent to which dentate gyrus volume can
differentiate between posttraumatic stress disorder- and depression-related
pathophysiology.
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