Cortical activation and functional connectivity during thumb-to-finger opposition in patients with stroke with varying functional levels: insights from fNIRS

Objective This study aimed to compare cortical activation and functional connectivity (FC) during a thumb-to-finger opposition task in stroke patients stratified by hand function level, and to explore the modulatory role of hand dominance.Methods Fifty-two right-handed stroke patients were divided into low-function (LFG, n = 28) and high-function (HFG, n = 24) groups based on task performance. Using 49-channel functional near-infrared spectroscopy (fNIRS), activation and FC were assessed in bilateral premotor/supplementary motor area (PMC&SMA), sensorimotor cortex (SMC), primary motor cortex (M1), and dorsolateral prefrontal cortex (DLPFC). Activation was analyzed via paired t-tests, FC matrices using Pearson’s correlation, and the effects of task and hand dominance via linear mixed models.Results Only the LFG showed a significant task-related increase in right DLPFC activation (q = 0.009), with a significant between-group difference (q = 0.019). FC analysis revealed stronger and more extensive connections in the HFG, particularly between M1 and PMC&SMA. In the LFG, FC significantly increased during the task (p = 0.006), and a significant task-by-hand dominance interaction was observed (p = 0.037), indicating that FC modulation depended on whether the affected hand was dominant. No such effects were found in the HFG.Conclusions Post-stroke functional level distinctly influences cortical activation and FC during fine motor tasks. Lower-function patients rely more on cognitive resources (DLPFC) and exhibit FC modulated by task demands and hand dominance, whereas higher-function patients demonstrate efficient integration within core motor networks. These findings support function-level-dependent neural reorganization and highlight the need for stratified, individualized rehabilitation strategies that consider both functional capacity and hand dominance.