Microelectrode array recordings from the ventral roots in chronically implanted cats.

Shubham Debnath,Matthew J Bauman,Robert A Gaunt,Douglas J Weber,Lee E Fisher

doi:10.3389/fneur.2014.00104

Abstract

The ventral spinal roots contain the axons of spinal motoneurons and provide the only location in the peripheral nervous system where recorded neural activity can be assured to be motor rather than sensory. This study demonstrates recordings of single unit activity from these ventral root axons using floating microelectrode arrays (FMAs). Ventral root recordings were characterized by examining single unit yield and signal-to-noise ratios (SNR) with 32-channel FMAs implanted chronically in the L6 and L7 spinal roots of nine cats. Single unit recordings were performed for implant periods of up to 12 weeks. Motor units were identified based on active discharge during locomotion and inactivity under anesthesia. Motor unit yield and SNR were calculated for each electrode, and results were grouped by electrode site size, which were varied systematically between 25 and 160 μm to determine effects on signal quality. The unit yields and SNR did not differ significantly across this wide range of electrode sizes. Both SNR and yield decayed over time, but electrodes were able to record spikes with SNR >2 up to 12 weeks post-implant. These results demonstrate that it is feasible to record single unit activity from multiple isolated motor units with penetrating microelectrode arrays implanted chronically in the ventral spinal roots. This approach could be useful for creating a spinal nerve interface for advanced neural prostheses, and results of this study will be used to improve design of microelectrodes for chronic neural recording in the ventral spinal roots.

Highlights

In 2005, nearly two million people in the United States were living with the loss of a limb, and it is projected that this number will double by 2050 [1] due to amputations following vascular disease, trauma, and cancer
In order to restore function to these individuals, neural interface technologies are being developed to enable intuitive control of robotic prostheses [2,3,4,5,6,7]. These neural interfaces extract control signals from the nervous system by decoding motor intent from the signals recorded in the brain [3, 4, 8, 9], peripheral nerves [2], or muscles [5, 10]
The ability to record action potentials from the axons of motor neurons in the ventral root was assessed by analyzing signal quality based on signal-to-noise ratios (SNR) and single unit yield over time

Summary

Introduction

In 2005, nearly two million people in the United States were living with the loss of a limb, and it is projected that this number will double by 2050 [1] due to amputations following vascular disease, trauma, and cancer. In order to restore function to these individuals, neural interface technologies are being developed to enable intuitive control of robotic prostheses [2,3,4,5,6,7]. These neural interfaces extract control signals from the nervous system by decoding motor intent from the signals recorded in the brain [3, 4, 8, 9], peripheral nerves [2], or muscles [5, 10]. There are well-established minimally invasive spine surgery procedures [11] that could potentially be adapted for implantation of electrodes in the spinal roots

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