Human balance is a complex process in healthy adults, requiring precisely-timed coordination between sensory information, cognitive processing, and motor control. It has been difficult to quantify brain dynamics during human balance control due to limitations in brain imaging modalities. The goal of this study was to determine if by using high-density electroencephalography (EEG) and independent component analysis, we can identify common cortical responses to visual and physical balance perturbations during walking and standing. We studied the responses of 30 healthy young adults to sensorimotor perturbations that challenged their balance. Subjects performed four 10-minute trials of beam-walking and tandem stance while either being mediolaterally pulled at the waist or viewing brief 20° field-of-view rotations in virtual reality. We recorded high-density EEG, motion capture, lower leg electromyography (EMG), and neck EMG. We hypothesized that both physical pull and visual rotation perturbations would elicit time-frequency fluctuations in theta (4-8 Hz) and beta (13-30 Hz) bands, with increased occipito-parietal activity during visual rotations compared to pull perturbations. Our results confirmed this hypothesis. For both perturbations, we found early theta synchronization and late alpha-beta (8-30 Hz) desynchronization following perturbation onset. This pattern was strongest in occipito-parietal areas during visual perturbations and strongest in sensorimotor areas during pull perturbations. These results suggest a similar time-frequency electrocortical pattern when humans respond to sensorimotor conflict, but with substantive differences in the brain areas involved for visual vs. physical perturbations. Our findings may have important implications for assessing and training balance in individuals with and without motor disabilities. Significance Statement We performed the first EEG time-frequency analysis on source-localized human electrocortical responses to physical and visual balance perturbations during both walking and standing. Perturbations elicited similar time-frequency patterns, but in notably different cortical areas for physical versus visual perturbations. Perturbation-evoked EEG fluctuations localized primarily to occipito-parietal areas during visual perturbations and motor areas during physical perturbations. These similarities suggest a common electrocortical response to sensorimotor perturbations. Notably, standing had greater electrocortical responses than walking. The results from this study may have applications in assessing and assisting treatment of balance dysfunction.
Peterson, S. M., & Ferris, D. P. (2018). Differentiation in theta and beta electrocortical activity between visual and physical perturbations to walking and standing balance. ENeuro, 5(4). https://doi.org/10.1523/ENEURO.0207-18.2018