Intracortical Microelectrode Array Unit Yield under Chronic Conditions: A Comparative Evaluation

Abstract

While microelectrode arrays (MEAs) offer the promise of elucidating functional neural circuitry and serve as the basis for a cortical neuroprosthesis, the challenge of designing and demonstrating chronically reliable technology remains. Numerous studies report “chronic” data but the actual time spans and performance measures corresponding to the experimental work vary. In this study, we reviewed the experimental durations that constitute chronic studies across a range of MEA types and animal species to gain an understanding of the widespread variability in reported study duration. For rodents, which are the most commonly used animal model in chronic studies, we examined active electrode yield (AEY) for different array types as a means to contextualize the study duration variance, as well as investigate and interpret the performance of custom devices in comparison to conventional MEAs. We observed wide-spread variance within species for the chronic implantation period and an AEY that decayed linearly in rodent models that implanted commercially-available devices. These observations provide a benchmark for comparing the performance of new technologies and highlight the need for consistency in chronic MEA studies. Additionally, to fully derive performance under chronic conditions, the duration of abiotic failure modes, biological processes induced by indwelling probes, and intended application of the device are key determinants.

Characterization of Active Electrode Yield for Intracortical Arrays: Awake versus Anesthesia

“…Our goal was to quantify the neurophysiological differences in single unit activity in the motor cortex of rats between conditions under anesthesia versus awake and freely behaving using intracortical silicon MEAs. We considered an early chronic period [ 7 ] post-implantation of MEAs and observed that the AEY was similar from these animals across the anesthetized and awake conditions. Furthermore, we noted a significantly higher SNR and lower noise levels for anesthetized recordings as compared to awake recordings.…”

“…The trauma from insertion as well as the continued presence of these devices elicit a foreign body response, resulting in macrophage and microglia activation, glial encapsulation, neuronal dieback, a breakdown of the blood–brain barrier [ 3 , 4 ], and oxidative stress [ 5 ] in the vicinity of the probe. Resulting degradation to the probe and adverse effects on the tissue cause an eventual decrease in long-term recording performance and reliability [ 4 , 6 , 7 ]. There are many approaches to mitigate the detrimental effects leading to MEA failure.…”

“…Metrics to assess chronic MEA reliability include the active electrode yield (AEY), i.e., the percentage of microelectrode sites that exhibit at least one discernable single unit, the signal-to-noise ratio (SNR), signal amplitude, and noise level. An important metric is AEY, which typically decreases significantly over implantation periods of several months [ 7 ]. In vivo experiments are the common method of testing the reliability and performance of these devices; however, the recording conditions vary among studies.…”

Ultraflexible and Stretchable Intrafascicular Peripheral Nerve Recording Device with Axon‐Dimension, Cuff‐Less Microneedle Electrode Array

“…Success of silicon-based microneedle electrodes can also be found for human electrophysiology research. [31,32] First, we used the device layer to fabricate the conductive silicon microneedle array with a series of customized deep reactive ion etching (DRIE) steps (Figure 2b-d) to create a sharp tip and several angles on the silicon microneedles, which we further describe in Figure S1, Supporting Information. The microneedle array was embedded partially in polydimethylsiloxane (PDMS).…”

“…Each electrode had an independent mechanical coupling to a low-modulus substrate. The design of microneedle nerve array (MINA) device was inspired by the success of the Utah array [30][31][32] and carbon fiber [9,26] particularly for the demonstrated mechanical robustness. Penetrating electrode arrays offer a larger spatial coverage of a small nerve than one transverse thin film array.…”