Exploring brain correlates of muscular activity and postural sway

Postural control indicates the ability to maintain stably our body in space and in time. This mechanism could be modelled as a dynamic feedback control system, where the central nervous system played a crucial role in ensuring the postural balance in standing position over time. Therefore, this work would insightfully explore this multimodal mechanism by combining information resulted from the simultaneous acquisition of postural, muscle and brain activity signals. Ten healthy volunteers were asked to stand with feet shoulder-width apart on a stable surface while keeping their eyes open for 30 s and postural sway parameters, lower limb muscle surface-electromyography (sEMG), and electroencephalography (EEG) signals were simultaneously recorded. Six global acceleration-domain postural sway parameters and two time-domain sEMG parameters for each leg muscle were extracted, while the EEG signals were processed to compute the functional brain connectivity matrices and to extract four global network graph theory (NGT) metrics, i.e., clustering coefficient, global efficiency, mean participation and assortativity. Spearman correlations were calculated and statistically significant negative correlation between postural sway parameters and, respectively, assortativity (p=-0.794) and global efficiency (p= -0.673) and between the muscle contraction of the soleus and the mean participation (respectively, p=-0.685, p=-0.697) emerged. These results suggested the importance of having efficient organization and a rapid adaptive mechanism of the brain to ensure a good level of stability, as well as a highly interconnected network to determine a higher level of stability with lower muscular contractions. Further analysis on larger datasets, also considering the contribution of the different EEG bands separately and the extraction of local NGT metrics, could bring out newer and compelling links between brain organization and functioning and the adopted postural strategy.