Spatio-temporal Dynamics of a Myelinated Nerve Fiber Model in Response to Staircase-shape Extracellular Electrical Stimulation

Abstract

It has been suggested that position- or diameter-selective recruitment of myelinated axons can be achieved by up-staircase-shape electrical nerve stimulation delivered from an extracellular electrode. However, so far, detail properties of the position- or diameter-selectivity of the stimulation have not been clarified. In this study, we investigated the spatio-temporal dynamics of myelinated axons in response to staircase-shape stimulation by numerical simulation of a compartmental model of rabbit myelinated axons. We found that the up-staircase-shape stimulation activates not only the targeted axons but also the ones close to the electrode by anodal break excitation;this property would degrade the distance selectivity of the stimulation. By considering the mechanism of extracellular electrical stimulation, we developed down-staircase-shape stimulation which can achieve selective activation of targeted axons without generating anodal break excitation near the electrode. Systematic simulation revealed that the down-staircase stimulation is better than the up-staircase one in terms of distance-selectivity of axon recruitment. However, diameter-selectivity of both stimulations was not sufficient.