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CHAPTER 3
2008). Studies in patients with dissociative disorders and co-morbid PTSD (Ehling, Nijenhuis & Krikke 2008, Irle et al. 2009, Stein et al. 1997, Tsai et al. 1999, Vermetten et al. 2006) have found smaller hippocampal volume in these individuals relative to HC, and one study (Ehling, Nijenhuis & Krikke 2008) reported a negative correlation between hippocampal volume and severity of life-time traumatizing experience and dissociative symptoms in individuals with Dissociative Identity Disorder (DID). DID is the most severe dissociative disorder, and has been conceptualized as a severe childhood-onset PTSD (Van der Hart, Nijenhuis & Steele 2006). Interestingly, hippocampal volume has been reported as preserved in patients with dissociative disorders without co-morbid PTSD (Weniger et al. 2008). Unfortunately, these studies suffered from several limitations: small sample sizes; inclusion of patients with mixed diagnoses of dissociative disorders without differentiating these groups within the analyses (DID, dissociative amnesia, dissociative disorder- not otherwise specified); and age differences between patients and controls (Ehling, Nijenhuis & Krikke 2008, Irle et al. 2009, Stein et al. 1997, Tsai et al. 1999, Vermetten et al. 2006, Weniger et al. 2008).
Most studies on the effects of early stress on the hippocampus, including those on PTSD or DID, have only examined differences in global hippocampal volume. However, the hippocampus consists of several histologically distinct subfields, each with distinct structural and functional connections with the cortex, specialized functional properties, and different developmental trajectories (Wang et al. 2010). In individuals from the general community, childhood traumatization (assessed using the Childhood Trauma Questionnaire (CTQ) (Bernstein et al. 1994) is specifically associated with relatively small volume within the CA2-3 (CA: cornu ammonis), CA4-DG (DG: dentate gyrus), subiculum, and to a lesser extent with smaller volume of the CA1 hippocampal subfields, revealing a relationship between childhood adversity maltreatment and small hippocampal subfield volumes (Teicher, Anderson & Polcari 2012). So far, only two studies evaluated hippocampal subfield volumes in PTSD patients (Bonne et al. 2008, Wang et al. 2010). These studies found smaller volume of the CA3/DG and posterior regions in PTSD patients compared with controls. However, these studies did not investigate the association with childhood traumatization or dissociative symptoms. Indeed, regional hippocampal volume and shape abnormalities have never been investigated in dissociative disorders.
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