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S.M. HIPPOCAMPAL MORPOHLOGY AND CHILDHOOD TRAUMA
good inter- and intra-rater reliabilities according to the established protocol (Thompson et al. 2004). The intraclass correlation coefficients for this rater were 0.94 and 0.97 for the left and right hippocampus, respectively, which are comparable to those in previously published studies (Cole et al. 2010). The outline of each hippocampus was traced in contiguous coronal brain sections while the digitized surface contours were displayed simultaneously in all three viewing planes to facilitate the accurate identification of boundaries (Thompson et al. 2004). Hippocampal global volumes obtained from these tracings were statistically analyzed.
To assess the shape deformations of different hippocampal subfields an anatomical surface mesh modeling method (Thompson et al. 2004) matched equivalent hippocampal surface points across subjects following manual tracing of the hippocampal boundaries. In brief: localized gray matter contractions and expansions of the hippocampal surface were established corresponding to the CA1, CA2-3 and subiculum (Figure 3.1a). In each individual the medial core, a central 3D curve threading down the long axis of the structure, was computed. From each point on the hippocampal surface a radial distance measure was derived to the medial core. As the same surface grid was imposed on all subjects’ hippocampi in the same coordinate space, statistical comparisons were made at each hippocampal surface point between the groups to index contrasts on a local scale. Probability values from these statistical comparisons were mapped onto an average hippocampal shape for the entire sample to generate a 3D representation of the structural differences between the groups. The approximate overlay of the hippocampal subfields was defined based on the Duvernoy atlas (Duvernoy 1988).
S3.2 Effect of medication
It has been reported that some psychiatric medications including typical antipsychotics (Chakos et al. 2005), anti-epileptics (Watanabe et al. 1992) and antidepressants (Vermetten et al. 2003) change the hippocampal morphology. In this study in order to ascertain genuine findings we repeated the analyses after excluding posttraumatic stress disorder patients with (PTSD-DID) or without (PTSD-only) dissociative identity disorder (DID) and a history of different types of psychiatric medications.
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