Elizabeth Pasman’s PhD Thesis Defence

Title:A Novel Approach to Studying Postural Instability in Parkinson’s disease”

Supervisory Committee: Dr. Mark Carpenter (Research Supervisor), Dr. Martin McKeown, Dr. J Timothy Inglis
University Examiners: Dr. John Kramer, Dr. Janice Eng
External Examiner: Dr. Alice Nieuwboer (KU Leuven, Belgium)
Chair: Dr. Miriam Spering

Abstract: Individuals with Parkinson’s disease (PD) often experience postural instability, a debilitating and largely treatment-resistant symptom. A better understanding of the neural substrates contributing to postural instability could lead to more effective treatments. However, investigating these neural substrates is made difficult by constraints of current functional neuroimaging techniques, such as the horizontal orientation of most MRI scanners. To address this constraint, we proposed to use a novel balance simulator that allows participants, while supine, to perform tasks that mimic free-standing balance. Overall, the general purpose of this thesis was to investigate the specific nature of balance deficits in PD, as well as the neural substrates contributing to postural instability in individuals with PD.

First, a systematic review of the literature was conducted to summarize the current evidence for the effect of PD, and the effect of antiparkinson treatment interventions, on static balance control. When focusing on studies that recorded quiet stance for at least 60 s, some consistent findings emerged that indicated individuals with PD display larger and faster sway compared to elderly controls, and that levodopa provides little improvement. Second, the MRI-compatible balance simulator was validated in individuals with PD and elderly controls. Results indicated that the simulator was easy to use for all participants, balance behaviour during the simulated balance tasks was similar to that seen during upright standing balance, and both static and dynamic balance deficits could be detected in the individuals with PD using the simulator. Finally, the simulator was used in the MRI scanner to investigate the neural substrates of static and dynamic balance deficits in PD using both brain connectivity and brain activation amplitude analyses. The connectivity analysis suggested elderly controls show a preference of subcortical over motor cortical control networks during dynamic balancing, while dynamic balance control in individuals with PD relies more on networks involving cortical (motor) areas. A similar pattern of results was seen for static balance during the brain activation amplitude analysis.

Overall, this thesis furthers our understanding of the specific nature of static balance deficits in individuals with PD, as well as the neural substrates underlying postural instability in PD.