Selectivity of afferent microstimulation at the DRG using epineural and penetrating electrode arrays

Abstract

Objective. We have shown previously that microstimulation of the lumbar dorsal root ganglia (L5-L7 DRG) using penetrating microelectrodes, selectively recruits distal branches of the sciatic and femoral nerves in an acute preparation. However, a variety of challenges limit the clinical translatability of DRG microstimulation via penetrating electrodes. For clinical translation of a DRG somatosensory neural interface, electrodes placed on the epineural surface of the DRG may be a viable path forward. The goal of this study was to evaluate the recruitment properties of epineural electrodes and compare their performance with that of penetrating electrodes. Here, we compare the number of selectively recruited distal nerve branches and the threshold stimulus intensities between penetrating and epineural electrode arrays. Approach. Antidromically propagating action potentials were recorded from multiple distal branches of the femoral and sciatic nerves in response to epineural stimulation on 11 ganglia in four cats to quantify the selectivity of DRG stimulation. Compound action potentials (CAPs) were recorded using nerve cuff electrodes implanted around up to nine distal branches of the femoral and sciatic nerve trunks. We also tested stimulation selectivity with penetrating microelectrode arrays implanted into ten ganglia in four cats. A binary search was carried out to identify the minimum stimulus intensity that evoked a response at any of the distal cuffs, as well as whether the threshold response selectively occurred in only a single distal nerve branch. Main results. Stimulation evoked activity in just a single peripheral nerve through 67% of epineural electrodes (35/52) and through 79% of the penetrating microelectrodes (240/308). The recruitment threshold (median = 9.67 nC/phase) and dynamic range of epineural stimulation (median = 1.01 nC/phase) were significantly higher than penetrating stimulation (0.90 nC/phase and 0.36 nC/phase, respectively). However, the pattern of peripheral nerves recruited for each DRG were similar for stimulation through epineural and penetrating electrodes. Significance. Despite higher recruitment thresholds, epineural stimulation provides comparable selectivity and superior dynamic range to penetrating electrodes. These results suggest that it may be possible to achieve a highly selective neural interface with the DRG without penetrating the epineurium.

The Effect of Clinically Controllable Factors on Neural Activation During Dorsal Root Ganglion Stimulation

“…Our data suggest that clinical DRGS directly activates myelinated neurons, regardless of electrode position, stimulation configuration, and stimulus pulse parameters (i.e., frequency, pulse width). This corroborates our previous study's findings that clinical DRGS is likely driving the activity of large‐diameter myelinated Aβ‐LTMRs, without directly activating small‐diameter nonmyelinated C‐nociceptors (19) and is supported by recent experimental findings that DRGS applied with nonpenetrating electrode arrays activates neurons with conduction velocities in the Aδ‐ to Aβ‐axon range (70). Furthermore, our data also suggest that clinical DRGS activates Aα‐neurons, and may activate Aδ‐neurons, though in a considerably smaller proportion than Aα‐ and Aβ‐neurons.…”

High-density spinal cord stimulation selectively activates lower urinary tract afferents

“…Therefore, we used stimulus-triggered averaging to detect responses evoked by stimulation. The presence of a compound action potential on each nerve was determined by comparing responses following stimulation to baseline recordings in which no stimulation occurred, using a previously-published method 67,68 . To determine the response detection threshold, we calculated the 99% confidence interval on the root mean squared baseline amplitude.…”

“…A binary search procedure was used to determine the minimum stimulus current necessary to recruit each nerve according to methods published previously 67,68 . First, we delivered 50 stimulation pulses through each electrode on the array in a random order using high amplitude pulses at 20 Hz to determine which electrodes could evoke responses in the peripheral nerves.…”

Stimulation of the Dorsal Root Ganglion using an Injectrode®

“…We filtered the ENG using a second-order high-pass filter with a cutoff frequency of 300 Hz, and we stimulation-triggered averaged the responses to 600 stimulus pulses. We determined the presence of an ECAP at a particular stimulation amplitude by comparing the root-mean-square (RMS) amplitude of the ENG to a threshold value, as shown in prior work (Ayers et al, 2016;Nanivadekar et al, 2019). We used a bootstrapping method to verify consistency of the evoked responses.…”