Brain white matter in the context of traumatic stress: a diffusion tensor imaging study

This body of research investigated brain white matter integrity in the context of Posttraumatic Stress Disorder (PTSD) and mild traumatic brain injury (mTBI). The overarching aim of this project was to identify and describe neural mechanisms associated with these two conditions. In order to achieve this, diffusion tensor imaging (DTI) was used to study microstructural profiles in four participant groups: (a) mTBI, (b) PTSD, (c) trauma-exposed controls, and (d) nontrauma-exposed controls. DTI is a structural imaging technique that provides information about the anatomical position, orientation and anisotropy of brains white matter neural tracts. Previous studies that have investigated neural mechanisms of traumatic stress have largely used healthy individuals with no prior exposure to psychologically traumatic events as a comparison group. Apart from including a group of healthy, non-trauma exposed volunteers, the present project also incorporated a group of participants with a history of trauma in order to control for the potential confounding effects of such prior experience. Based on past research, this study selected three white matter tracts that have been previouslyimplicated in PTSD, mTBI or both. Study 1 investigated microstructure of the corpus callosum.This tract was characterized by compromised integrity in both PTSD and mTBI. Study 2 examined the underlying structure of the cingulum bundle. mTBI showed aberrant changes that were not observed in PTSD. Study 3 investigated white matter coherence within the uncinate fasciculus. Neither mTBI nor PTSD were associated with microstructural alterations within this tract. Finally, Study 4 explored individual contributions of PTSD severity and history of mTBI to the observed microstructural damage within the corpus callosum and cingulum. Global anisotropy changes within the corpus callosum were shown to be associated with both factors. Alterations within the cingulum, however, were only predicted by a history of mTBI. Overall, the findings from this thesis indicated that while the corpus callosum showed vulnerability to the effects of both PTSD and mTBI, changes within the cingulum bundle appeared to be only mediated by a history of mTBI

Dysregulation in cortical reactivity to emotional faces in PTSD patients with high dissociation symptoms

Background: Predominant dissociation in posttraumatic stress disorder (PTSD) is characterized by restricted affective responses to positive stimuli. To date, no studies have examined neural responses to a range of emotional expressions in PTSD with high dissociative symptoms. Objective: This study tested the hypothesis that PTSD patients with high dissociative symptoms will display increased event-related potential (ERP) amplitudes in early components (N1, P1) to threatening faces (angry, fearful), and reduced later ERP amplitudes (Vertex Positive Potential (VPP), P3) to happy faces compared to PTSD patients with low dissociative symptoms. Methods: Thirty-nine civilians with PTSD were classified as high dissociative (n=16) or low dissociative (n=23) according to their responses on the Clinician Administered Dissociative States Scale. ERPs were recorded, whilst participants viewed emotional (happy, angry, fear) and neutral facial expressions in a passive viewing task. Results: High dissociative PTSD patients displayed significantly increased N120 amplitude to the majority of facial expressions (neutral, happy, and angry) compared to low dissociative PTSD patients under conscious and preconscious conditions. The high dissociative PTSD group had significantly reduced VPP amplitude to happy faces in the conscious condition. Conclusion: High dissociative PTSD patients displayed increased early (preconscious) cortical responses to emotional stimuli, and specific reductions to happy facial expressions in later (conscious), face-specific components compared to low dissociative PTSD patients. Dissociation in PTSD may act to increase initial pre-attentive processing of affective stimuli, and specifically reduce cortical reactivity to happy faces when consciously processing these stimuli