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HIPPOCAMPAL MORPOHLOGY AND CHILDHOOD TRAUMA
(Teicher, Anderson & Polcari 2012, Wang et al. 2010). Elevated levels of stress hormones can result in reduced branching of dendrites, reduced synaptic plasticity, neuronal loss or suppression of neurogenesis (Sapolsky 1993). The CA2-3 and subiculum subfields have the highest density of glucocorticoid receptors (Sarrieau et al. 1986) and hence are the most susceptible subfields to the adverse effect of stress. The CA1 neurons in the anterior hippocampus in humans project to the medial prefrontal cortex (Small et al. 2011). The morphological abnormalities of this subfield could perhaps indicate a potential disturbance in the prefrontal-limbic system, including in the regulation of the hypothalamic-pituitary-adrenal (HPA) axis during stress (Herman et al. 2005). Therefore, they could possibly be, at least in part, related to the HPA axis dysfunction reported in the patients with PTSD (for a review see de Kloet et al. (2006)) or with a dissociative disorder (Simeon et al. 2007). The dentate gyrus is involved in neurogenesis and it has been suggested that childhood traumatization can suppress neurogenesis and hence result in smaller CA4- dentate gyrus subfield (Teicher, Anderson & Polcari 2012). This is of course conjecture and the direct relationship between hippocampal morphometric abnormalities and these stress hormone pathways and neuronal properties would need to be confirmed experimentally.
Our finding of a relationship between abnormalities of global and subfield hippocampal volume and severity of childhood traumatizing events in DID, provides a first neuroanatomical support for the hypothesis that the pathophysiology of DID is related to childhood traumatization (Van der Hart, Nijenhuis & Steele 2006, Reinders et al. 2003, Reinders et al. 2006, Reinders et al. 2012). Although, the present findings need to be confirmed by other neuroanatomical studies, they are in line with the negative correlations previously reported between severity of childhood traumatizing events and hippocampal global (Andersen et al. 2008, Dannlowski et al. 2012, Samplin et al. 2013) and subfield (Teicher, Anderson & Polcari 2012) volumes in adults from the general community with a history of early-life adversity. However, as the current study is a cross-sectional study we could not examine direct or indirect links between these measures and hence longitudinal studies are needed to further explore these.
In the two patient groups, severity of dissociative symptom was negatively correlated with the volume of presubiculum and the subiculum, but not with global hippocampal volumes. So far, limited studies have investigated this
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