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Degree

Doctor of Philosophy

Program

Psychology

Supervisor

Adrian M. Owen

Abstract

Some patients with disorders of consciousness retain sensory and cognitive abilities that are not apparent from their outward behaviour. It is crucial to identify and characterise these covert abilities for diagnosis, prognosis, and medical ethics. This thesis uses neuroimaging techniques to investigate cognitive preservation and awareness in patients who are behaviourally non-responsive due to acquired brain injuries. In the first chapter, a large sample of healthy volunteers, including experienced athletes and musicians, imagined actions of varying complexity and familiarity. Motor imagery involving certain complex, familiar actions correlated with a more robust sensorimotor rhythm. In the second chapter, several patients with disorders of consciousness participated in multiple experiments based on neural responses to mental imagery, including one task featuring complex, familiar imagined actions. Although the patients did not generate enhanced sensorimotor rhythms for the complex, familiar motor imagery, the detection of covert cognition was more sensitive owing to the multi-modal nature of the assessment. In the final empirical chapter, a sample of healthy volunteers and a heterogeneous cohort of patients with disorders of consciousness completed a novel oddball task based on tactile stimulation. Critically, this task delineated an attentional hierarchy in the patient sample, and patients with the ability to follow commands were differentiated from those unable to do so by event-related potential evidence of attentional orienting. Due to the heterogeneity of aetiology and pathology in the disorders of consciousness, these patients vary in their suitability for neuroimaging, the preservation of neural structures, and the cognitive resources available to them. Assessments of several perceptual and cognitive abilities supported by spatially-distinct brain regions and indexed by multiple neural signatures are therefore required to accurately characterise a patient’s abilities and probable subjective experience.

Summary for Lay Audience

Some patients with disorders of consciousness retain sensory and cognitive abilities that are not apparent from their outward behaviour. It is crucial to identify and characterise these covert abilities for diagnosis, prognosis, and medical ethics. This thesis uses neuroimaging techniques to investigate cognitive preservation and awareness in patients who are behaviourally non-responsive due to acquired brain injuries. In the first chapter, a large sample of healthy volunteers, including experienced athletes and musicians, imagined actions of varying complexity and familiarity. Motor imagery involving certain complex, familiar actions correlated with a more robust sensorimotor rhythm. In the second chapter, several patients with disorders of consciousness participated in multiple experiments based on neural responses to mental imagery, including one task featuring complex, familiar imagined actions. Although the patients did not generate enhanced sensorimotor rhythms for the complex, familiar motor imagery, the detection of covert cognition was more sensitive owing to the multi-modal nature of the assessment. In the final empirical chapter, a sample of healthy volunteers and a heterogeneous cohort of patients with disorders of consciousness completed a novel oddball task based on tactile stimulation. Critically, this task delineated an attentional hierarchy in the patient sample, and patients with the ability to follow commands were differentiated from those unable to do so by event-related potential evidence of attentional orienting. Due to the heterogeneity of aetiology and pathology in the disorders of consciousness, these patients vary in their suitability for neuroimaging, the preservation of neural structures, and the cognitive resources available to them. Assessments of several perceptual and cognitive abilities supported by spatially-distinct brain regions and indexed by multiple neural signatures are therefore required to accurately characterise a patient’s abilities and probable subjective experience.

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