Electronic Thesis and Dissertation Repository

Degree

Master of Science

Program

Neuroscience

Supervisor

Adrian Owen

Abstract

Diagnosing disorders of consciousness (DOC) is notoriously difficult, with estimates of misdiagnosis rates as high as 40%. Moreover, recent studies have demonstrated that patients who do not show signs of volitional motor responses can exhibit preserved command following detected by functional magnetic resonance imaging (fMRI) and electroencephalography (EEG). Although these patients clearly retain some cognitive abilities, lack of consistent motor responses makes administration of standard neuropsychological tests impossible. Consequently, the extent of their cognitive function is unknown. In the current study, we developed and validated a P300b event related potential (ERP) neuropsychological battery in healthy participants to assess components of executive function without requiring motor output. First, participants were instructed to attend to a target auditory stimulus. P300b responses to attended relative to unattended stimuli were used as a neural proxy for detecting command following. To assess working memory capacity we adapted a digit span test to use a similar P300b response mechanism. Finally, reasoning was assessed by adapting a verbal reasoning task in the same manner. At the group level, and in a large majority of participants at the single-participant level, accurate performance could be detected using the P300b ERP, validating the potential utility of the battery. Additionally, the normalized magnitude of the P300b predicted individual differences in performance, but only when a suitable level of variability between participants was present. A post hoc Monte Carlo analysis was conducted to examine the necessary time required to conduct the battery as well as the interaction between time and performance in determining statistically significant performance. At 100% accuracy, a mean time of five minutes was required to achieve a significant result, with time increasing as a function of decreasing performance. These results demonstrate that covert control of attention, as measured by the P300b ERP, can be used to assess command following, working memory and reasoning abilities with a high degree of reliability


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