Event-related Potential Markers of Perceptual and Conceptual Speech Processes in Patients with Disorders of Consciousness.

Vegetative state (VS) and minimally conscious state (MCS) patients behaviorally demonstrate absent or fluctuating levels of awareness. Functional magnetic resonance imaging evidence of covert perceptual and semantic speech processing provides prognostic value for these patients. In this thesis, I examined the utility of high-density electroencephalography (EEG) in this regard. A contrast between event-related potentials (ERPs) elicited by primed and unprimed word pairs was used to isolate conceptual (semantic) processes, while ERPs elicited by signal-correlated noise were contrasted with those elicited by speech to isolate pre-semantic, perceptual aspects of speech processing. These ERP effects were found to be both temporally and spatially dissociable, indicating the contributions of not entirely overlapping regions of cortex. Four out of ten VS/MCS patients demonstrated significant perceptual effects, while no conceptual effects were observed for any patient. It is therefore possible to identify low-level stages of language processing that can now be tested for prognostic value given future follow-up studies