Simultaneous monitoring of the human brain, spinal cord, and cauda equina activity for movement control: An fNIRS approach

Brain‒spinal cord‒cauda equina interactions are essential for controlling lower body movement. However, current monitoring approaches for spinal and caudal activity are limited to use without body movement and to processing via batches of data. Here, we present a novel optical method based on functional near-infrared spectroscopy that enables simultaneous tracking of human brain-spinal cord-cauda equina hemodynamics during body movement. We first developed a support frame for positioning optical emitters and receivers along the spinal canal to maximize spatial resolution and identify the optimal distance between them. We tested the methodology at this optimal emitter-detector distance by assessing the spatiotemporal activation of the motor clusters associated with human ankle extension-flexion movement in the brain, spinal cord, and cauda equina. These brain and spinal clusters are shown to be functionally connected and comparable to those identified by invasive methods during surgical operations. These findings suggest that hemodynamic responses reflect synchronous neural activity in the human brain-spinal cord-cauda equina system for hindlimb movement control.