Imaging Brain Responses to Spinal Neuromodulation: Validation of a Custom LSCI System for Cerebral Perfusion Mapping in Healthy Rats

Cervical spinal cord stimulation (SCS) has emerged as a promising neuromodulatory technique capable of modulating cerebral blood flow (CBF), yet its cortical and vascular effects remain underexplored. In this study, we developed and applied a dual-wavelength laser speckle contrast imaging (LSCI) system to quantify the spatial, temporal, and compartment-specific impact of cervical SCS on cerebral perfusion in anesthetized healthy rats. High-resolution speckle flow index (SFI) data were acquired bilaterally from secondary motor (M2), primary motor (M1), and primary somatosensory (S1) cortices, targeting arteries, veins, and microvascular tissue. Stimulation was delivered unilaterally at the C1–C2 spinal levels using amplitudes of 100, 300, and 500 µA across three durations (1, 3, and 5 minutes). SCS induced robust increases in CBF that were strongly phase-dependent and varied by amplitude and anatomical location. Venous and parenchymal structures exhibited the largest flow enhancements, particularly in M1 and S1 regions. Flow changes were consistently greater in the right hemisphere, regardless of stimulation side. Among stimulation intensities, 500 µA elicited the highest absolute SFI increases, while 300 µA yielded sustained and physiologically stable responses with minimal post-stimulation overshoot. Dual-wavelength imaging further revealed local increases in hemoglobin oxygenation during and after stimulation, supporting an active hemodynamic mechanism. Additionally, vein diameter measurements confirmed significant post-stimulation vascular dilation, with the greatest diameter expansion (+29.2%) observed in the right S1 cortex. These findings demonstrate that cervical SCS modulates cortical perfusion in a region-, structure-, and hemisphere-specific manner. This work establishes a reproducible, high-resolution imaging framework for investigating the cerebral effects of spinal cord neuromodulation and provides foundational evidence for optimizing stimulation parameters for future clinical applications targeting cortical blood flow regulation.