Cognitive-Motor Dual-Task Cost in Individuals with Multiple Sclerosis

Multiple sclerosis (MS) is a neurodegenerative disease that negatively impacts various cognitive and motor aspects. It has been extensively shown that individuals with MS perform worse when completing a motor task and cognitive task simultaneously (dual-tasking), than when they perform a single task. Dual-tasking is a very common aspect of daily life, and any deficits increase fall risk, which consequently reduces quality of life. Research in this area adopts a dual-task paradigm in which performance while dual-tasking is compared to performance while single-tasking to assess a dual-task cost (DTC), or a decrease in function while dual-tasking. Most research to date has focused on the motor outcome measures during dual-tasking and there is a current lack of understanding in how the cognitive outcome measures are affected. The present study assessed cognitive performance during dual-tasking compared to single-tasking for several challenging tasks. Additionally, blood flow to the pre-frontal cortex (PFC) in the brain was measured using functional near-infrared spectroscopy (fNIRS) during this procedure. Measuring blood flow to the brain can be used as a proxy for neuronal activation, so this data provided a more nuanced understanding of how dual-tasking affects brain physiology in individuals with MS. We hypothesized that there would be heightened PFC activation during dual-tasking in individuals with MS compared to single-tasking across all tasks. We also hypothesized that there would be an inverse relationship between PFC activation and cognitive/motor outcomes during dual-tasking, meaning that as PFC activation increased, cognitive and motor performance variables would decrease. The results show increased PFC activation while performing cognitive single-tasks compared to dual-tasks, but decreased PFC activation while performing motor single-tasks compared to dual-tasks. Cognitive measures and motor outcomes decreased while dual-tasking, compared to single-tasking. This suggests that dual-tasking is challenging enough to cause these individuals to reach attentional capacity, and most likely other brain areas increase activation during dual-tasking to compensate. Additionally, motor DTCs were greater than cognitive DTCs, which suggests a cognitive-task prioritization. More research must be conducted investigating other brain areas to get a better insight to the functional brain mechanisms of individuals with MS and the task prioritization strategy they adopt while performing demanding and ecologically valid dual-tasks