Analysis of Corticomuscular Coherence between Motor Cortex Region and Tibialis Anterior Muscle Using Symbolic Transfer Entropy

Corticomuscular coherence reveals how the brain motor cortex and muscles communicate. It plays a paramount role in the analysis of movement-related neurological and neuromuscular disorders. The coherence is usually measured from simultaneous electroencephalography (EEG) and electromyography (EMG) signals. These signals are nonlinear, and therefore the extraction of reliable information is considered to be a challenging task. Symbolic transfer entropy (STE) is a nonlinear technique for capturing the signals' wide dynamic properties. The corticomuscular coherence has been estimated from EEG to EMG signals using STE in this study. For this purpose, the simultaneous EEG to EMG activities of ten healthy subjects recorded during standing, level walking, stair descending, stair descending, ramp descending, and ramp ascending are considered. The symbolic transfer entropy is extracted from the EEG signals associated with the motor cortex region (C1, C2, and Cz.) and EMG signal of the Tibialis Anterior (TA) muscle. In addition, a frequency domain-based coupling strength is also calculated to analyze the interactions between brain and muscle. The results show that there exists notable bidirectional coherence and corticomuscular coupling between the electrical activities of the brain to the muscular system. EMG to EEG has a higher STE and coupling strength than EEG to EEG. The findings also show that the suggested STE method is capable of describing the coherence and information exchange between the motor cortex and muscles.