Corticocortical and Corticomuscular Connectivity Dynamicsin Standing Posture: Electroencephalography Study

Cortical involvements, including those in the sensorimotor, frontal, and occipitoparietal regions, are important mechanisms of neural control in human standing. Previous research has shown that cortical activity and corticospinal excitability vary flexibly in response to postural demand. However, it is unclear how corticocortical and corticomuscular connectivity is dynamically modulated during standing balance and over time. This study investigated the dynamics of this connectivity using electroencephalography (EEG) and electromyography (EMG). The EEG and EMG were measured in different 4 positions: sitting (ST), normal quiet standing (QS), one-leg standing (ON), and standing on a piece of wood (WD). For corticomuscular connectivity, we concentrated on sway-varying connectivity in the timing of peak velocity of postural sway in the anteroposterior direction. For the corticocortical connectivity, the time-varying connectivity was quantified, particularly in the {theta}-band connectivity which is linked to error identification, using a sliding-window approach. The study found that corticomuscular connectivity from the brain to the lower-limb muscle was strengthened during the sway peak in the {gamma}- and {beta}-frequency bands, while the connectivity strength from the muscle to the brain was decreased in the {theta}- and -band. For the time-varying connectivity, the {theta}-connectivity in all time-epoch was divided into 7 states including both posture-relevant and -irrelevant clusters. In one of the 7 states, the strong connectivity pairs were concentrated in the mid-central region and the proportion of epochs from the ON and WD conditions was significantly higher, indicating a functional role for posture balance. These findings shed light on electrodynamic connectivity which varies in response to postural demand. Those dynamics, particularly in the {theta}-band connectivity, can be used for ongoing monitoring and/or intervention for postural disability.