Detecting Command-Driven Brain Activity in Patients with Disorders of Consciousness Using TR-fNIRS

Vegetative state (VS) is a disorder of consciousness often referred to as “wakefulness without awareness”. Patients in this condition experience normal sleep-wake cycles, but lack all awareness of themselves and their surroundings. Clinically, assessing consciousness relies on behavioural tests to determine a patient’s ability to follow commands. This subjective approach often leads to a high rate of misdiagnosis (~40%) where patients who retain residual awareness are misdiagnosed as being in a VS. Recently, functional neuroimaging techniques such as functional magnetic resonance imaging (fMRI), has allowed researchers to use command-driven brain activity to infer consciousness. Although promising, the cost and accessibility of fMRI hinder its use for frequent examinations. Functional near-infrared spectroscopy (fNIRS) is an emerging optical technology that is a promising alternative to fMRI. The technology is safe, portable and inexpensive allowing for true bedside assessment of brain function. This thesis focuses on using time-resolved (TR) fNIRS, a variant of fNIRS with enhanced sensitivity to the brain, to detect brain function in healthy controls and patients with disorders of consciousness (DOC). Motor imagery (MI) was used to assess command-driven brain activity since this task has been extensively validated with fMRI. The feasibility of TR-fNIRS to detect MI activity was first assessed on healthy controls and fMRI was used for validation. The results revealed excellent agreement between the two techniques with an overall sensitivity of 93% in comparison to fMRI. Following these promising results, TR-fNIRS was used for rudimentary mental communication by using MI as affirmation to questions. Testing this approach on healthy controls revealed an overall accuracy of 76%. More interestingly, the same approach was used to communicate with a locked-in patient under intensive care. The patient had residual eye movement, which provided a unique opportunity to confirm the fNIRS results. The TR-fNIRS results were in full agreement with the eye responses, demonstrating for the first time the ability of fNIRS to communicate with a patient without prior training. Finally, this approach was used to assess awareness in DOC patients, revealing residual brain function in two patients who had also previously shown significant MI activity with fMRI