A Theoretical Study of Epidural Electrical Stimulation of the Spinal Cord - Part II: Effects on Long Myelinated Fibers

This second paper, of two, draws upon earlier finite element solutions for electrical fields generated within the spinal cord by epidural electrodes. Given those fields, a lumped network model of the myelinated nerve axon is used to predict stimulation thresholds for afferent fiber pathways in the dorsal columns and dorsal roots. Threshold predictions for dorsal column fibers of 5 and 10 , im diameters correspond closely with sensory thresholds reported experimentally. Descending fibers in the lateral corticospinal tracts are also considered. Comparisons are made to other possible targets of stimulation, and the theoretical indications are discussed in the context of clinical findings.