Does impedance matter when recording spikes with polytrodes?

Abstract

Extracellular microelectrodes have been widely used to measure brain activity, yet there are still basic questions about the requirements for a good extracellular microelectrode. One common source of confusion is how an electrode's impedance affects the amplitude of extracellular spikes and background noise.Here we discuss how an electrode's impedance affects data quality in extracellular recordings, which is crucial for both the detection of spikes and their assignment to the correct neurons. This study employs commercial polytrodes containing 32 electrodes (177 µm 2 ) arranged in a dense array. This allowed us to directly compare, side-by-side, the same extracellular signals measured 2 by modified low impedance (~100 kOhm) microelectrodes with unmodified high impedance (~1 MOhm) microelectrodes. We begin with an evaluation of existing protocols to lower the impedance of the electrodes. The poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT-PSS) electrodeposition protocol is a simple, stable, and reliable method for decreasing the impedance of a microelectrode up to tenfold. We next record in vivo using polytrodes that are modified in a 'chess board' pattern, such that the signal of one neuron is detected by multiple coated and non-coated electrodes. The performance of the coated and non-coated electrodes is then compared on measures of background noise and amplitude of the detected action potentials.If the proper recording system is used, then the impedance of a microelectrode within the range of standard polytrodes (~ 0.1 to 2 MOhm) does not significantly affect data quality and spike sorting.This study should encourage neuroscientists to stop worrying about one more unknown.

Flexible Multielectrode Arrays With 2-D and 3-D Contacts for $In~ Vivo$ Electromyography Recording

“…9(a) denote the standard error of mean. The lower SNR of the 2-D electrodes can be attributed to the higher electrode impedance due to the lower surface area [33]- [35]; the 3-D electrodes, on the other hand, provide a larger surface area with the same footprint as that of 2-D electrodes which in turn results in a lower electrode impedance and a higher SNR. Furthermore, since the 2-D electrodes are inset below the top insulation layer, they are also more susceptible to protein buildup on the electrode surface during the course of an in vivo measurement, which also translates into a higher electrode impedance.…”

Does Impedance Matter When Recording Spikes With Polytrodes?

“…We would like to thank the institutional support and funding provided by the Champalimaud Foundation, CENIMAT/I3N and Sainsbury Wellcome Centre (funded by the Gatsby Charitable Foundation and the Wellcome Trust). An earlier version of this work has been released as a preprint ( Neto et al, 2018 ).…”

Fabrication of a Multilayer Implantable Cortical Microelectrode Probe to Improve Recording Potential

“…This can be accomplished by electroplating gold or conductive polymers such as poly (3,4-ethylenedioxythiophene) (PEDOT) layers of varying thickness onto the electrode surfaces from different layers. The use of PEDOT may not only compensate for the distance differences of electrodes to firing neurons, but also provide a more intimate contact between the electrode surface and the soft brain tissue [76], since these polymers have substantially lower Young's modulus than metal.…”