Altered Sensorimotor Lateralization and Cross-modal Consistency in Stroke: A Simultaneous EEG–fNIRS Study

Stroke often leads to motor impairment and is associated with disruptions in sensorimotor pathways and altered cortical lateralization. Although understanding these changes is essential for interpreting post-stroke neural reorganization, it remains unclear whether they are consistently reflected at both neural and hemodynamic levels. This study aimed to investigate cross-modal consistency using simultaneous electroencephalography (EEG) and functional near-infrared spectroscopy (fNIRS). EEG and fNIRS signals were recorded from stroke patients and age-matched healthy controls during unilateral handgrip tasks. Event-related desynchronization (ERD) and oxygenated hemoglobin (HbO) responses were used to compute the lateralization index (LI), and a cross-modal lateralization consistency index (cmLCI) was proposed to quantify EEG-fNIRS correspondence. Results showed that, in stroke patients, HbO responses exhibited significantly greater contralateral than ipsilateral activation during both affected- and unaffected-hand movements (p < 0.001), whereas LI showed no significant differences between patients and healthy controls. In the beta band, ERD was significantly lower in the contralateral than ipsilateral hemisphere during affected-hand movement (p = 0.002), with a reduced LI compared with the unaffected-hand condition (p < 0.001). Furthermore, cmLCI in the alpha and beta bands was significantly reduced in the affected-hand condition (p < 0.01). Importantly, beta-band cmLCI during affected-hand movement was positively correlated with Fugl-Meyer scores (R² = 0.32, p = 0.018). These findings reveal altered sensorimotor lateralization electrophysiological-hemodynamic and consistency reduced after stroke. The proposed cmLCI captures these alterations and is associated with clinical motor impairment, supporting its potential as a multimodal indicator of post-stroke cortical reorganization and motor impairment.