A Primary Study on Ipsilateral Motor Cortex Activation During Unilateral Hand Movements Using EEG-fNIRS-sEMG

Upper limb movements can be associated with activation of both sensorimotor cortices on functional MRI. The neurophysiological significance of the ipsilateral activation remains unclear. This study aimed to understand changes in ipsilateral motor cortical (iM1) activation during finger and shoulder movements. Fourteen healthy subjects were recruited and were asked to perform two experiments in left- and right-hand. Experiment 1 required the execution of hand clenching task, and experiment 2 consisted of shoulder forward flexion and elbow flexion. During motor execution, electroencephalography (EEG) and functional near-infrared spectroscopy (fNIRS) and surface electromyography (sEMG) data were simultaneously recorded. EEG analysis was employed to assess event-related desynchronization (ERD), fNIRS to measure blood oxygen concentrations (oxygenated hemoglobin, HbO) in the brain, and sEMG to analyze the electrical activity of muscles during movement. ERD occurred clearly bilaterally during both shoulder and elbow movements compared to hand clenching. In all left-hand conditions, the HbO was significantly higher contralaterally than ipsilaterally (P < 0.05). Additionally, hand clenching exhibited significantly higher HbO and muscle electrical activity compared to shoulder and elbow movements (P < 0.05). Ipsilateral ERD and HbO during execution appear to reflect the excitability of proximal muscle and the level of muscle activation, respectively. This information may be valuable for comprehensively studying movement disorders, like those in post-stroke hemiplegic patients.