Tuning Microelectrodes’ Impedance to Improve Fast Ripples Recording

TL;DR

This study shows that coating microelectrodes with a conductive polymer improves the recording of fast ripples, which are important biomarkers for identifying seizure-causing brain areas in epilepsy.

Contribution

The novel use of a conductive polymer coating on microelectrodes significantly enhances fast ripple observability in epileptic mice.

Findings

PEDOT:PSS-coated electrodes had two orders of magnitude lower impedance than uncoated ones.

Coated electrodes showed higher transfer function amplitude and cut-off frequency.

FRs recorded with coated electrodes had significantly higher signal energy.

Abstract

Epilepsy is a chronic neurological disorder characterized by recurrent seizures resulting from abnormal neuronal hyperexcitability. In the case of pharmacoresistant epilepsy requiring resection surgery, the identification of the Epileptogenic Zone (EZ) is critical. Fast Ripples (FRs; 200–600 Hz) are one of the promising biomarkers that can aid in EZ delineation. However, recording FRs requires physically small electrodes. These microelectrodes suffer from high impedance, which significantly impacts FRs’ observability and detection. In this study, we investigated the potential of a conductive polymer coating to enhance FR observability. We employed biophysical modeling to compare two types of microelectrodes: Gold (Au) and Au coated with the conductive polymer poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (Au/PEDOT:PSS). These electrodes were then implanted into the CA1 hippocampal neural network of epileptic mice to record FRs during epileptogenesis. The results showed that the polymer-coated electrodes had a two-order lower impedance as well as a higher transfer function amplitude and cut-off frequency. Consequently, FRs recorded with the PEDOT:PSS-coated microelectrode yielded significantly higher signal energy compared to the uncoated one. The PEDOT:PSS coating improved the observability of the recorded FRs and thus their detection. This work paves the way for the development of signal-specific microelectrode designs that allow for better targeting of pathological biomarkers.

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