This thesis presents research aimed at elucidating neurophysiological and neuropsychological correlates of two psychiatric disorders, schizophrenia and PTSD. Although psychiatric disorders are not traditionally known for featuring cognitive deficits, research over the past three decades has revealed that deficits in many aspects of cognitive functioning are present across a wide range of disorders. Here, we aim to further our understanding of these deficits and provide evidence of the clinical utility of neurophysiological correlates of cognitive dysfunction. The cause and course of cognitive deficits in PTSD is poorly understood, and an investigation of one potential explanatory mechanism, dissociative symptomatology, is presented in the first part of this thesis. Our results suggest that dissociative symptomatology plays a role in cognitive dysfunction in PTSD, as among the clinical variables tested (including PTSD symptomatology, dissociative symptoms, depressive symptoms, and anxiety symptoms) dissociative symptoms were the only significantly correlated variables to cognitive dysfunction in a sample of combat-trauma exposed veterans with and without PTSD. In the second part of this thesis, we investigate the potential clinical utility of a neurophysiological biomarker for semantic processing deficits, the N400, in schizophrenia. Our results indicate that N400 measures are stable over a one week period and therefore may be clinically useful as a neurophysiological biomarker for semantic processing abnormalities in schizophrenia. Overall, these two studies contribute to our knowledge of cognitive deficits in psychiatric disorders and demonstrate their complexity as well as their potential to provide clinically useful tools to aid in the identification of novel treatments targeted at ameliorating cognitive deficits in schizophrenia and PTSD.

Master of Science (MSc)

Thesis