Optimal Electrode Size for Multi-Scale Extracellular-Potential Recording From Neuronal Assemblies

Abstract

Advances in microfabrication technology have enabled the production of devices containing arrays of thousands of closely spaced recording electrodes, which afford subcellular resolution of electrical signals in neurons and neuronal networks. Rationalizing the electrode size and configuration in such arrays demands consideration of application-specific requirements and inherent features of the electrodes. Tradeoffs among size, spatial density, sensitivity, noise, attenuation, and other factors are inevitable. Although recording extracellular signals from neurons with planar metal electrodes is fairly well established, the effects of the electrode characteristics on the quality and utility of recorded signals, especially for small, densely packed electrodes, have yet to be fully characterized. Here, we present a combined experimental and computational approach to elucidating how electrode size, and size-dependent parameters, such as impedance, baseline noise, and transmission characteristics, influence recorded neuronal signals. Using arrays containing platinum electrodes of different sizes, we experimentally evaluated the electrode performance in the recording of local field potentials (LFPs) and extracellular action potentials (EAPs) from the following cell preparations: acute brain slices, dissociated cell cultures, and organotypic slice cultures. Moreover, we simulated the potential spatial decay of point-current sources to investigate signal averaging using known signal sources. We demonstrated that the noise and signal attenuation depend more on the electrode impedance than on electrode size, per se , especially for electrodes <10 μm in width or diameter to achieve high-spatial-resolution readout. By minimizing electrode impedance of small electrodes (<10 μm) via surface modification, we could maximize the signal-to-noise ratio to electrically visualize the propagation of axonal EAPs and to isolate single-unit spikes. Due to the large amplitude of LFP signals, recording quality was high and nearly independent of electrode size. These findings should be of value in configuring in vitro and in vivo microelectrode arrays for extracellular recordings with high spatial resolution in various applications.

Neural signal recording and processing in somatic neuroprosthetic applications. A review

“…A common assumption is that large electrodes (> 50 μm in diameter) are adequate for recording compound field potentials from a wide neuronal ensemble, while small electrodes (< 20 μm) are more suitable for recording extracellular action potentials generated by few nearby neurons (Rossant et al, 2016). Using arrays containing platinum electrodes of different sizes, it was found that noise and signal attenuation depend more on the electrode impedance than on electrode size; by reducing the impedance of small electrodes by surface modifications, the SNR of axonal action potentials was increased (Viswam et al, 2019). For this reason current micro-electrodes design presents macroporous structures in order to maximize surface for signal acquisition.…”

Active plasmonic nanoantenna: an emerging toolbox from photonics to neuroscience

“…Wellestablished semiconductor industry manufacturing capabilities allow recording electrodes to be reduced in size and integrated with high density using complementary metaloxide-semiconductor (CMOS) technology. However, implementing extremely small metal electrodes poses an enormous challenge due to parallel interfacing requirements imposed by relatively sizable peripheral recording electronics that secure the connections between multiplexed inputs and outputs [261,267,268]. Due to this fundamental bottleneck, multiplexed measurement capabilities of MEAs have been limited [267].…”

Recording site placement on planar silicon-based probes affects neural signal quality: edge sites enhance acute recording performance

“…The influence of size, impedance and material of recording sites on neural recordings is relatively well studied [30][31][32][33]. However, prior research investigating the optimal placement of recording sites on silicon shanks to achieve high quality recordings is scarce and contradictory [34][35][36].…”