| Description |
The research detailed within this dissertation investigates the neurobiological changes associated with emotional processing of backward masked emotional faces in veterans with and without posttraumatic stress disorder (PTSD). PTSD affects millions of Americans, including approximately 20% of veterans, and is associated with a number of negative symptoms, including hyperarousal, avoidance, and flashbacks. In this dissertation, we examined a group of 15 veterans with PTSD and a group of 12 veterans without PTSD using both functional magnetic resonance imaging (fMRI) and electroencephalography (EEG). Using fMRI, the blood oxygen level dependent (BOLD) signal of the amygdala and extrastriate cortex was measured, and using EEG, the P1 event-related potential (ERP) was recorded in response to masked affect. The veteran group with PTSD exhibited increased extrastriate BOLD signal but decreased P1 ERP amplitude in the right hemisphere. This was evidence of a right hemisphere specific visuosensory modulation in veterans with PTSD, which is most evident using EEG. Unexpectedly, the P1 ERP and extrastriate BOLD signal did not display a significant linear relationship in either veteran group, which indicates that although activity was measured from similar regions, the two methodologies provided distinct information regarding neuronal activity in this study. In addition, a relationship was observed between the BOLD signal of the amygdala and extrastriate cortex and the degree of combat exposure, based on the Combat Exposure Scale (CES). A veteran group without PTSD displayed a negative correlation between the extent of combat exposure and amygdalar BOLD activity. This was not the case for a veteran group with PTSD, who instead exhibited a negative correlation between the degree of combat exposure and extrastriate BOLD activity. When the total score of the CES was used as a covariate, the veteran group with PTSD displayed significantly increased amygdalar BOLD and extrastriate BOLD activity, compared to the veteran group without PTSD. This research highlights the importance of multimodal research, as differences between the two groups were observed using both methodologies. Our results suggest a relationship between the degree of combat exposure and the processing of masked emotional stimuli, even in veterans without PTSD. |
