| dc.description.abstract | Parkinson’s disease (PD) is the second most common neurodegenerative disease in the world. Individuals with PD are at high risk of falling due to degeneration of dopaminergic and cholinergic pathways in the basal ganglia. The risk of falling increases when performing two tasks simultaneously, such as standing while talking. In such dual-tasking conditions, upright stance posture is an essential motor skill to accomplish various motor and cognitive tasks concurrently. Although maintaining an upright stance posture seems autonomous and effortless in healthy individuals, it may become challenging and cognitively effortful due to impaired autonomic control processes in individuals with PD. Dual-tasking deficiency is operationally defined as a decrease in motor or cognitive performance (or both) when tasks are performed concurrently. Dual-tasking deficiency is observed in all humans, but individuals with PD seem to be disproportionally affected by dual-tasking due to competition of limited cognitive resources. Dual-tasking is typically evaluated by dual-task cost on either cognitive tests or balance measures. However, these common endpoints have methodological limitations (ceiling/floor effect), they are not sensitive to change, and they do not explain the amount of cognitive workload needed to complete the tasks. Based on attention and effort theory, cognitive workload is defined as the mental effort that is needed to execute a task. Advances in neurophysiological technology enable us to measure cognitive workload in real-time. Pupillary response is a non-intrusive, real-time neurophysiological measure of cognitive workload. This dissertation project examined the neurophysiological response of the brain measured by pupillary response during dual-tasking conditions in individuals with PD. In Chapter 2, we conducted a systematic review to investigate the real-time brain activity during dual task gait and balance and whether changes in brain activity correlate with changes in behavioral outcomes in older adults and people with age-related neurodegenerative conditions. In Chapter 3, we investigated the usefulness of pupillary response to quantify the cognitive workload of postural control in healthy young adults. In Chapter 4, we examined the reliability and validity of pupillary response during dual-task balance conditions in individuals with PD. Finally, in Chapter 5, we conducted a study to investigate neurophysiological changes, indexed by pupillary response, during dual-task balance between three groups: PD fallers; PD non-fallers; and healthy controls. This body of research extends the use of pupillary response as a metric of cognitive workload during cognitive testing to cognitive-motor testing in a rehabilitation research setting. To our knowledge, this is the first study that investigated pupillary response as a metric of cognitive workload during dual-task balance in healthy adults and individuals with PD. Previous studies mainly used functional near-infrared spectroscopy or electroencephalogram as a neurophysiological tool to understand brain activity in aging and age-related neurodegenerative conditions. Pupillary response is cost-effective, less intrusive, and easy to implement in clinical settings compared to electroencephalogram and functional near-infrared spectroscopy. We found that pupillary response is a reliable and valid measure of cognitive workload during dual-task balance in both healthy adults and in individuals with PD. In addition, the findings of this research project demonstrated that individuals with PD exhibited higher cognitive workload measured by pupillary response compared to age- and sex-matched healthy controls during dual-task balance. Lastly, pupillary response significantly increased with increased task difficulty especially from single task to dual-task balance as well as from eyes open to eyes occluded conditions in both individuals with PD and healthy controls. | |
