Page 49 - PIECES OF THE PUZZLE Eline Vissia

HIPPOCAMPAL MORPOHLOGY AND CHILDHOOD TRAUMA
Statistical analysis
The effect of PTSD diagnosis was first investigated on the global hippocampal and subfield volumes by comparing volumetric measurements between All-PTSD and HC. To this end, a repeated-measures analysis of covariance (ANCOVA) was used with hemisphere (left or right) as the repeated measure and age and parenchymal volume as covariates. The analysis was then followed by pairwise t-tests to compare left and right hippocampal volumes separately between: 1) PTSD-DID vs. HC, 2) PTSD-DID vs. PTSD-only, and 3) PTSD-only vs. HC. Furthermore, in order to ascertain that our findings are not due to the differences in the medication usage between the groups, these analyses were repeated after excluding the patients with a history of using different types of psychiatric medications (see supplementary material S3.2: Tables S3.1-S3.3).
To assess regional hippocampal shape deformations, statistical regression analyses, with age and parenchymal volume as covariates, were conducted at each hippocampal surface point to map the associations between group and radial distance, a measure of local hippocampal shape. The resulting statistical maps (P-map) of group differences (uncorrected) were displayed on the hippocampal surface template, which was created by averaging hippocampal shapes from the entire sample. Furthermore, permutation tests with 10,000 iterations and a threshold of p<0.05 were run to obtain an omnibus corrected p-value for each P-map.
In the All-PTSD group, we tested the association of severity of childhood traumatizing events with global hippocampal and subfield volumes using partial correlations while controlling for age and parenchymal volume. Furthermore, a possible link between global and subfield hippocampal volumes and severity of dissociative symptoms was tested using partial correlations while adjusting for age and parenchymal volume.
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