Cortical beta oscillatory activity evoked during reactive balance recovery scales with perturbation difficulty and individual balance ability

Abstract

I.AbstractCortical beta oscillations (13-30 Hz) reflect sensorimotor cortical activity, but have not been fully investigated in balance recovery behavior. We hypothesized that more challenging balance conditions would lead to greater recruitment of cortical sensorimotor brain regions for balance recovery. We predicted that beta power would be enhanced when balance recovery is more challenging, either due to more difficult perturbations or due to lower intrinsic balance ability. In 19 young adults, we measured beta power evoked over motor cortical areas (Cz electrode) during 3 magnitudes of backward support-surface translational perturbations using electroencephalography. Peak beta power was measured during early (50-150 ms), late (150-250 ms), and overall (0-400 ms) time bins, and wavelet-based analyses quantified the time course of evoked beta power and agonist and antagonist ankle muscle activity. We further assessed the relationship between individual balance ability measured in a challenging beam walking task and perturbation-evoked beta power within each time bin. In balance perturbations, cortical beta power increased ∼50 ms after perturbation onset, demonstrating greater increases with increasing perturbation magnitude. Balance ability was negatively associated with peak beta power in only the late (150-250 ms) time bin, with higher beta power in individuals who performed worse in the beam walking task. Additionally, the time course of cortical beta power followed a similar waveform as the evoked muscle activity, suggesting these evoked responses may be initially evoked by shared underlying mechanisms. These findings support the active role of sensorimotor cortex in balance recovery behavior, with greater recruitment of cortical resources under more challenging balance conditions. Cortical beta power may therefore provide a biomarker for engagement of sensorimotor cortical resources during reactive balance recovery and reflect the individual level of balance challenge.

Prefrontal-motor and somatosensory-motor cortical network interactions during reactive balance are associated with distinct aspects of balance behavior in older adults

“…We then computed the mean baseline beta power (-500 to 0ms before perturbation onset) and the peak of the perturbation-evoked change in beta power (100-500ms) relative to baseline for each participant. Based on our previous study which found differences between early and later portions of motor cortical beta activity responses as a function of balance ability in younger adults (Ghosn et al, 2020), we further identified peak perturbation-evoked beta power within an early (100-300ms) and later (300-500ms) time window of the response.…”

“…Twenty-four perturbations of equal magnitude (7.5 cm, 16.0 cm/s, 0.12 g) were delivered in the forwards direction to elicit a backwards center of mass displacement relative to the base of support. The scaling of these perturbation parameters was selected to ensure that platform deceleration did not occur until 500 ms after perturbation onset to minimize changes in cortical and motor output originating from a deceleration response (Ghosn et al, 2020;McIlroy & Maki, 1994). Because we aimed for each participant to sustain identical perturbations, we selected this lower-level perturbation magnitude as a level of postural destabilization that could be successfully completed by most older adults using a feet-in-place strategy (Figure 1).…”

“…In the present study, we aimed to quantify individual reactive balance capacity by increasing the magnitude of balance perturbations to the point where balance challenge exceeded the capacity for an individual to produce feet-in-place reactions, necessitating a later-phase reactive stepping response that is likely cortically-mediated (B. E. Maki & McIlroy, 2007). Previously, our lab used EEG to assess cortical activity during balance reactions in younger adults and found larger evoked cortical responses in individuals with lower balance performance on a beam walking task (Ghosn et al, 2020;. Further, evoked cortical activity was dissociable from evoked muscle activity, suggesting a potential cortical motor contribution to later-phase reactive balance control (Payne et al, 2019).…”

“…E. Maki & McIlroy, 2007). Previous studies have identified active cortical regions during continuous balance and walking tasks in older adults (Chang et al, 2016;Malcolm et al, 2020), but cortical oscillatory activity time-locked to destabilizing balance events, shown to be associated with balance ability in younger adults (Ghosn et al, 2020), or interactions between cortical regions reflecting information processing and integration during motor behavior have not been well investigated in older adults, who have increasing risk for falling with age. Such knowledge could identify effective neural control strategies during balance-correcting behavior in high-functioning older adults, and could be leveraged towards the development of precision medicine approaches for individualized fall prevention strategies among a heterogeneous older adult population.…”

“…We aimed to characterize the neural dynamics of cortical oscillatory activity and interactions between cortical regions during balance reactions, and test the relationship between individual cortical engagement strategy during balance reactions and distinct aspects of balance behavior that are predictive of falls in older adults. used EEG to assess cortical activity during balance reactions in younger adults and found larger evoked cortical responses in individuals with lower balance performance on a beam walking task (Ghosn et al, 2020;. Further, evoked cortical activity was dissociable from evoked muscle activity, suggesting a potential cortical motor contribution to later-phase reactive balance control (Payne et al, 2019).…”