Load-dependent Motor Cortical Activation Assessed by fNIRS Is Partially Preserved After Stroke

OBJECTIVE: The aim of this study was to investigate whether patients with stroke retain proportional hemodynamic cortical responses to increasing mechanical loading during upper limb exercise. DESIGN: Twelve patients with stroke and twelve healthy control subjects participated in this cross-sectional comparative study. Patients with stroke performed repetitive upper limb lifting tasks with loads of 0, 1, and 2 kg, whereas healthy subjects lifted loads of 0, 3, and 15 pounds. Hemodynamic cortical responses were measured during four repetitions of each load condition presented in randomized blocks. RESULTS: In patients with stroke, a significant linear relationship between load magnitude and cortical activation was observed only in the ipsilesional posterior parietal cortex (PPC). No significant proportional load-related responses were detected in other motor-related cortical regions. In contrast, healthy subjects demonstrated significant load-dependent increases in cortical activation in the contralateral primary motor cortex, supplementary motor area, premotor cortex, and PPC. CONCLUSIONS: Patients with stroke preserve proportional load-related hemodynamic responses in the PPC but not in primary motor cortical areas, suggesting a compensatory role of the PPC. These findings highlight the PPC as a potential target for monitoring cortical engagement and for neuromodulation strategies in upper limb stroke rehabilitation.