Microelectrode Array Recordings from the Ventral Roots in Chronically Implanted Cats

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.

Rodent model for assessing the long term safety and performance of peripheral nerve recording electrodes

“…Through post-hoc data analysis, the threshold for impedance change that signifies a nonfunctional array was 3x the average pre-implantation impedance. The vulnerability of lead wires to breakage has been reported both in animal models (Branner et al, 2004, Kung et al, 2014, Prasad et al, 2014), and in human experiments (Davis et al, 2016, Debnath et al, 2014), and should be a focus for improvements in electrode design.…”

“…Alternative approaches use intraneural electrodes, such as microelectrode arrays and thin films electrodes, to penetrate the nerve and access individual axons, allowing for higher selectivity (Badia et al, 2011, Branner and Normann, 2000). Examples include longitudinal intrafascicular electrodes (LIFE) (Lawrence et al, 2004, Rossini et al, 2010), transverse intrafascicular multichannel electrode (TIME) (Boretius et al, 2010), Utah arrays (Branner and Normann, 2000, Clark et al, 2011), and floating microelectrode arrays (FMA) (Debnath et al, 2014). A major challenge with intraneural electrodes has been poor long-term stability due to multiple factors, including device reliability and nerve fiber damage due to electrode motion inside the nerves (Grill et al, 2009, Saal and Bensmaia, 2015).…”

Chronic monitoring of lower urinary tract activity via a sacral dorsal root ganglia interface

“…B. Dorsal view of penetrating microelectrode arrays implanted unilaterally in left S1 and S2 DRG in four felines. C. Custom acrylic backpack housing (top) based on previous designs [42,43]. The backpack with cover removed (bottom left).…”

Heuristic Spike Sorting Tuner (HSST), a framework to determine optimal parameter selection for a generic spike sorting algorithm

“…The HSST framework was also tested on real neural data consisting of 80 datasets recorded from microelectrodes implanted in the dorsal root ganglion (DRG) of a cat's L6 and L7 spinal roots (Debnath et al, 2014). For these real world datasets, no ground truth existed; thus, expert human sorters identified all units with an SNR greater than 5, calculated as the ratio of peak signal voltage to estimated peak noise voltage.…”