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

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.

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.

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.

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.