Corticomuscular coupling alterations during task-dependent bimanual coordination after stroke: A multimodal...

Post-stroke bimanual coordination dysfunction severely impairs activities of daily living. However, the underlying neurophysiological mechanisms remain incompletely understood, particularly regarding central-peripheral coupling characteristics under different bimanual coordination tasks and their distinction from aging effects. This study included 32 chronic subcortical stroke patients and 29 healthy controls. Functional near-infrared spectroscopy and surface electromyography signals were synchronously acquired during the execution of symmetrical and asymmetrical bimanual coordination tasks. Analyzed indices included cortical activation patterns, functional connectivity, corticomuscular coupling characterized by transfer entropy, intermuscular coupling, and muscle synergies. Correlations between these indices and the Fugl-Meyer Assessment for Upper Extremity and Modified Barthel Index were also evaluated. The results showed that during the symmetrical task, the ascending muscle-to-cortex connectivity was significantly reduced in the patient group, and this index was significantly positively correlated with the Modified Barthel Index. Brain functional connectivity and cortical activation were significantly increased in the patient group, and the connectivity from the ipsilesional prefrontal cortex to the contralesional SAC was significantly negatively correlated with Fugl-Meyer Assessment for Upper Extremity scores. Additionally, intermuscular coupling was significantly weakened, and muscle synergy patterns were abnormal in the patient group. During the asymmetrical task, no significant group differences in corticomuscular coupling were found, but brain functional connectivity and cortical activation were both significantly increased, and the connectivity from the ipsilesional supplementary motor area to the contralesional supplementary motor area was significantly positively correlated with MBI. Intermuscular coupling was significantly weakened, and muscle synergy patterns were abnormal. Attribution analysis suggested that cortical hyperactivation patterns and abnormal muscle synergies mainly reflect stroke effects, while abnormal sensory cortex activation and altered corticomuscular coupling may be influenced by both stroke and aging. This study suggests that post-stroke bimanual coordination impairment is closely related to selective damage to sensory feedback pathways, manifested as task-dependent reductions in ascending (muscle-to-cortex) corticomuscular coupling and compensatory cortical reorganization. Multimodal neurophysiological indicators may serve as potential quantitative tools for assessing upper limb function after stroke, but age-matched control studies are essential to dissociate stroke effects from aging effects.