Somatosensory impairment among people with multiple sclerosis may worsen cognitive and physical fatigue, and exacerbate balance dysfunction

About This Grant

PROJECT SUMMARY Multiple sclerosis (MS) is a chronic and debilitating disease of the nervous system that has widespread effects, impacting physical and mental function. Among the most common symptoms experienced by people with MS (PwMS) are balance dysfunction and fatigue, rated as having the most profound negative impacts on quality of life. Although evidence suggests that fatigue and balance dysfunction are related, the specific mechanism that determines this relationship among PwMS is not known. However, evidence supports somatosensory impairment as a major contributor to balance dysfunction and fatigue among PwMS; we hypothesize that somatosensory impairments mediate increased attentional and physical demands that drive cognitive and physical fatigue, thereby increasing MS-related fatigue. The somatosensory system is vital to postural coordination because it is the most sensitive sensory modality to postural instability; thus, degraded or delayed somatosensory feedback leads to greater postural instability that must be counteracted by the neuromuscular system to maintain balance. We hypothesize that this requires increased motor output to prevent balance loss, increasing the physical load and consequently physical fatigue. Although somatosensory feedback is degraded among PwMS, we believe that compensatory mechanisms attempt to mitigate these effects; these include compensation by other sensory modalities (primarily vision), referred to as sensory reweighting, and greater attentional resources to maintain balance. We hypothesize that these compensations require additional cognitive resources that lead to increased cognitive fatigue. To test these hypotheses, we will systematically assess balance tasks that will increase the physical load, cognitive load and available sensory feedback to directly evaluate somatosensory impairment as a mediator of physical and cognitive fatigue, and balance dysfunction in PwMS. This study will leverage advances in wearable motion-tracking technologies to quantify postural sway dynamics, and portable functional near infrared spectroscopy to quantify changes in cortical blood flow indicative of changes in cortical activation. Thus, we will assess changes in the motor cortex related to physical load, the dorsolateral prefrontal cortex (which directs attentional resources to balance control) related to cognitive load, and the visual cortex to evaluate sensory reweighting. These measures, paired with subjective and objective assessment of fatigue, will provide new mechanistic insight into the role of somatosensory impairment in modulating balance dysfunction and fatigue. The expected outcomes of this research include: a new target for early therapeutic intervention that could mitigate MS-related fatigue and balance dysfunction, and improve quality of life among those with MS; and determination of potential differential impacts of somatosensory loss on balance and fatigue among nonprogressive and progressive MS subtypes—knowledge that could aid in identifying and tracking progression among those with MS.