Corticomuscular coupling alterations in subacute stroke patients: insights from fNIRS and sEMG

Corticomuscular coupling (CMC) reflects the neural communication between the central and peripheral nervous systems, particularly during motor control. However, the corticomuscular coupling characteristics during upper limb motor tasks in stroke patients remain unclear. This study aims to explore the differences in corticomuscular coupling characteristics between stroke patients and healthy subjects.

A total of 25 stroke patients in the subacute phase with dominant hemisphere and 20 age-matched healthy controls were enrolled in the study. Participants performed an isometric wrist extension task at 50% of their maximum voluntary contraction (MVC) for 15 s, during which surface electromyography (sEMG) signals measured from the flexor carpi radialis and extensor carpi ulnaris, as well as functional near-infrared spectroscopy (fNIRS) data from the prefrontal cortex, supplementary motor area, and primary motor cortex, were simultaneously recorded. Corticomuscular coupling metrics (phase synchronization index (PSI), coherence), fNIRS measures (cortical activation, functional connectivity), and sEMG parameters (root mean square (RMS), median frequency (MF), and fuzzy approximate entropy (fApEn)) were analyzed.

Stroke patients demonstrated significantly reduced PSI and coherence values in specific corticomuscular couplings compared to age-matched healthy controls. Moreover, enhanced cortical activation, stronger functional connectivity, and diminished muscle activation (with lower sEMG complexity) were observed in specific cortical regions and assessed muscles.

This study reveals differences in the mapping relationship between cortical activation and sEMG signals across time-domain and frequency-domain indices in stroke patients compared to healthy subjects, providing new theoretical insights into the interaction between brain activity and motor execution. These results underscore the disrupted corticomuscular coupling in stroke patients and suggest its value in characterizing the central-peripheral interaction during motor execution, which may inform future rehabilitation assessment strategies.