Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Psychology

Supervisor

Owen, Adrian M.

2nd Supervisor

Stojanoski, B.

Co-Supervisor

Abstract

Standardized behavioural assessments of awareness remain the gold standard for patients with disorders of consciousness (DOC) and inform diagnosis, prognosis, and medical decision-making. However, recent neuroimaging research has identified a small but significant number of DOC patients who retain perceptual and cognitive abilities not evidenced by their behaviour. Therefore, it is imperative to develop assessment techniques to identify and characterize the conscious experiences of patients with DOC. This thesis presents a novel movie-based electroencephalographic (EEG) assessment of perceptual and cognitive function in DOC patients. In Chapter 2, we calculated EEG inter-subject correlations (ISCs) in healthy controls and DOC patients to index higher-order “executive” processing of two types of movie stimuli (audio-visual, audio-only). Contrary to their behavioural diagnosis, 25% and 30% of patients showed preserved perceptual and cognitive abilities necessary to process the audio-visual and auditory movies, respectively. In Chapter 3, we determined whether a translated version of the auditory movie could be used to assess French-speaking populations of DOC patients. Here, two groups of healthy controls (English and French-speaking) showed comparable degrees of ISCs that occurred at roughly the same timepoints across languages. In Chapter 4, we explored the prognostic utility of ISCs, functional connectivity, and source localized EEG activity in a cohort of patients with severe acute brain injury. ISCs and functional connectivity, but not source localized activity, were marginally predictive of outcomes after severe brain injury. Over three studies, we developed and validated a novel EEG assessment of perceptual and cognitive function in DOC patients, demonstrated its potential application in English and French populations, and established the feasibility of this assessment in acutely brain-injured patients.

Summary for Lay Audience

Disorders of consciousness (DOC) are a class of neurological disorders that can result from severe brain injury. Patients with DOC exhibit minimal behavioural evidence that they are aware of themselves or their environment; they may appear to be awake but fail to respond to stimulation or verbal command. However, DOC are diagnosed solely on the basis of observable behaviour, which may be impaired in patients with severe brain injury. Recent neuroimaging research has identified a small but significant number of DOC patients who show neural evidence of conscious awareness, despite remaining behaviourally non-responsive. One method to uncover the neural correlates of awareness in DOC patients is to use movie stimuli and track patients’ neural responses to elements of the story like its suspense, which cannot be processed unconsciously. This thesis presents a novel movie-based electroencephalographic (EEG) assessment of residual awareness in patients with DOC. In Chapter 2, we calculated EEG inter-subject correlations (ISCs) between healthy controls and patients with DOC to compare the similarity of their neural responses during two movie types (audio-visual, audio only). Overall, 25% and 30% of patients produced neural activity that closely resembled healthy controls—suggesting a comparable degree of narrative processing—during the audio-visual and audio movie, respectively. In Chapter 3, we compared EEG activity across English and French-speaking healthy controls to determine whether a translated (to French) version of the auditory movie assessment was suitable for French-speaking DOC patients. Here, both groups produced comparable degrees of ISCs that occurred at roughly the same time points, thereby validating this assessment for French-speaking populations of DOC patients. In Chapter 4, we explored whether the auditory movie could help predict recovery from recent serious brain injury. We found that ISCs and EEG functional connectivity were marginally associated with survival. Over three studies, we developed and validated a novel EEG assessment of awareness in DOC patients, demonstrated its potential application in English and French populations, and established the feasibility of this assessment in recently brain-injured patients.

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