Individual-specific engagement of cortical resources for standing balance control in aging and post stroke

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Project Summary Our long-term goal is to identify neural mechanisms of healthy and impaired balance to guide mechanistically- based predictors, assessments, and interventions for addressing balance and gait impairments common in aging and neurological disorders. It is well-known clinically that engagement of cortical resources in balance control is an indicator of fall risk in older adults including stroke survivors, as inferred by the degradation of balance and/or gait performance when a concurrent cognitive task shifts attention away from balance control. A scientific barrier to improving prognostic tools, preventive strategies, and interventions for balance impairments is that we lack an understanding of how and when cortical resources are engaged in balance control, particularly with balance task difficulty. An innovation of our proposal is to identify direct, mechanistic measures of cortical activity during reactive balance. We will combine MPI Ting’s expertise in the neuromechanics of reactive balance control and MPI Borich’s expertise in human electrophysiology to identify relationships between brain activity and motor function to improve stroke rehabilitation. Our objective is to identify cortical activity signatures that distinguish individual-, task-, and group-level differences in the engagement of cortical resources for balance control amongst young adults (Aim 1), older adults (Aim 2), and older adults with unilateral lesions due to stroke (Aim 3). We will measure electroencephalographic (EEG), electromyographic (EMG), and biomechanical signals during reactive balance recovery to support-surface translations. We propose to use both clinically feasible electrode-based analysis approaches, as well as mechanistically-important anatomically-informed functional analyses using high-density EEG in combination with structural and functional MRI scans. We hypothesize that cortical activity signatures during balance control increase in an individual-, age-, and disease-specific manner as balance task difficulty increases. Within groups, we predict individual variability in cortical activity to be explained by balance challenge, i.e., balance task difficulty normalized to step threshold, a measure of balance function. However, between groups, we predict cortical activity signatures and their relation to balance challenge will differ. Our Aims are motivated by our preliminary data that show 1) increases in N1 and beta power over leg sensorimotor regions with balance task difficulty depend on balance function in young and older adults 2) opposite relationships between sensorimotor functional connectivity and balance task difficulty in younger vs. older adults; 3) distinct aspects of balance function associated with sensorimotor vs. prefrontal-motor connectivity in older adults; and 4) sensorimotor functional connectivity in stroke survivors associated with walking function. If successful, we will identify neurophysiological indicators of balance health that will be broadly applicable across the lifespan, and across neurological and orthopedic balance disorders to significantly advance the scientific framework to enable precision-medicine strategies for personalized, mechanistic assessments and interventions to improve quality of life those with poor balance health.