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CHAPTER 3
11.37%) as well as compared with PTSD patients without DID (PTSD-only) (left: 7.25%; right: 6.58%). The PTSD-only group showed a trend level difference in the right global hippocampal volume when compared with HC (right: 5.13%; p=0.067), and post hoc analyses (see supplementary material S3.3) revealed that bilateral hippocampi were significantly smaller in those PTSD-only patients with a history of childhood onset traumatizing events (left: 7.11%; right: 7.31%), suggesting again that childhood traumatization is an important factor in the hippocampal abnormalities. These findings concur with prior neuroimaging studies in adult victims of childhood adversity, with or without PTSD (Andersen et al. 2008, Bremner et al. 2003) and in DID patients (Ehling, Nijenhuis & Krikke 2008, Irle et al. 2009, Stein et al. 1997, Tsai et al. 1999, Vermetten et al. 2006). Also, our findings support and advance a previous report of smaller hippocampal volume in DID patients with co-morbid PTSD (Vermetten et al. 2006) which was limited by the unmatched characteristics of their control group (Vermetten 2006), an issue we did not have in this study.
Smaller hippocampal volumes were particularly located in the subfields CA1, CA2-3, CA4-DG, and (pre)subiculum, a finding also supported by shape analysis results. The subiculum has specifically been associated with memory retrieval, whereas regions corresponding to CA2-3 are involved in the encoding of episodic information (Eldridge et al. 2005). The role of CA1 in encoding and retrieval of contextual memory has been reported in animal studies (Daumas et al. 2005). Therefore, abnormalities of any of these subfields could result in memory abnormalities and the localized deformations and gray matter loss in different hippocampal subfields observed in PTSD-DID and PTSD- only patients could underlie memory alterations reported in DID patients (Dorahy 2001) and the impaired (non-)declarative memory often reported in PTSD patients (for review see (Samuelson 2011)). Our study opens avenues to investigate the cognitive correlates of hippocampal abnormalities and we suggest that future research investigate the relationship between memory performance and hippocampal abnormalities in DID and PTSD with childhood traumatizing events.
Our findings of smaller volume and deformed shape of the hippocampal subfields in PTSD patients with childhood adversity and in DID patients are consistent with evidence of a relationship between stress and/or elevated level of glucocorticoids (the main stress-related hormones) and morphological alteration of the hippocampal CA1, CA2-3, CA4-DG and (pre)subiculum subfields
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