Imaging fast neural traffic at fascicular level with electrical impedance tomography: proof of principle in rat sciatic nerve

Camille Blochet,David Holder,Kirill Aristovich,Sana Hannan,James Avery,Daniel J Chew,Matteo Donegá

doi:10.1088/1741-2552/aad78e

Abstract

Objective. Understanding the coding of neural activity in nerve fascicles is a high priority in computational neuroscience, electroceutical autonomic nerve stimulation and functional electrical stimulation for treatment of paraplegia. Unfortunately, it has been little studied as no technique has yet been available to permit imaging of neuronal depolarization within fascicles in peripheral nerve. Approach. We report a novel method for achieving this, using a flexible cylindrical multi-electrode cuff placed around nerve and the new medical imaging technique of fast neural electrical impedance tomography (EIT). In the rat sciatic nerve, it was possible to distinguish separate fascicles activated in response to direct electrical stimulation of the posterior tibial and common peroneal nerves. Main results. Reconstructed EIT images of fascicular activation corresponded with high spatial accuracy to the appropriate fascicles apparent in histology, as well as the inverse source analysis (ISA) of compound action potentials (CAP). With this method, a temporal resolution of 0.3 ms and spatial resolution of less than 100 µm was achieved. Significance. The method presented here is a potential solution for imaging activity within peripheral nerves with high spatial accuracy. It also provides a basis for imaging and selective neuromodulation to be incorporated in a single implantable non-penetrating peri-neural device.

Highlights

There is currently renewed interest in the coding of neural information in the field of computational neuroscience
Electrical impedance tomography (EIT) is an emerging medical imaging method in which small changes in impedance of a conductive volume may be imaged with an array of external electrodes
This requires averaging over some tens of seconds or minutes in response to repeated evoked activity, but delivers a final data set with images every millisecond of neuronal depolarisation in the field of interest

Summary

Introduction

There is currently renewed interest in the coding of neural information in the field of computational neuroscience. Information is transmitted to the central nervous system through peripheral nerves and any complete description requires understanding of spike coding in nerve as well as brain [2] This field is not well developed, which may be attributed to limitations in technology for recording such neural activity within nerves. We have extended its use to imaging the CAP in peripheral nerve using a non-penetrating soft rubber external nerve cuff with 16–32 electrodes (16 were used in this study as a proof of concept, 32 is currently being investigated) It yields images of CAP volleys with fascicles in the nerve with a resolution of

Methods

Results

Conclusion