A model of electrical impedance tomography on peripheral nerves for a neural-prosthetic control interface

TL;DR

This paper presents a neural-EIT model for peripheral nerves, demonstrating its potential to record neural activity using a novel electrode pattern, advancing neural prosthetic interface technology.

Contribution

It extends neural-EIT modeling to myelinated fibers in peripheral nerves and proposes a new electrode pattern for activity differentiation.

Findings

Unmyelinated fiber activity can be screened out above 100 Hz

Impedance changes during neural activity are quantified at 1 kHz

A novel electrode pattern can distinguish fascicle activity

Abstract

Objective: A model is presented to evaluate the viability of using electrical impedance tomography (EIT) with a nerve cuff to record neural activity in peripheral nerves. Approach: Established modelling approaches in neural-EIT are expanded on to be used, for the first time, on myelinated fibres which are abundant in mammalian peripheral nerves and transmit motor commands. Main results: Fibre impedance models indicate activity in unmyelinated fibres can be screened out using operating frequencies above 100 Hz. At 1 kHz and 10 mm electrode spacing, impedance magnitude of inactive intra-fascicle tissue and the fraction changes during neural activity are estimated to be 1,142 {\Omega}.cm and -8.8x10-4, respectively, with a transverse current, and 328 {\Omega}.cm & -0.30, respectively with a longitudinal current. We show that a novel EIT drive and measurement electrode pattern which utilises longitudinal current and longitudinal differential boundary voltage measurements could distinguish activity in different fascicles of a three-fascicle mammalian nerve using pseudo-experimental data synthesised to replicate real operating conditions. Significance: The results of this study provide an estimate of the transient change in impedance of intra-fascicle tissue during neural activity in mammalian nerve, and present a viable EIT electrode pattern, both of which are critical steps towards implementing EIT in a nerve cuff for neural prosthetics interfaces.