Carbon and metal microelectrodes for recording of epileptic High Frequency Oscillations: a comparative study

High Frequency Oscillations (HFO: 80–600 Hz) and particularly Fast-Ripples (FRs: 200–600 Hz) gained increasing interest over the last decade as a biomarker of epileptogenic networks. FRs were shown to be generated by small clusters of weakly synchronized hyperexcitable neurons, the recording of which requires the use of intracerebral microelectrodes. Nonetheless, the detection of FRs recorded using classical metal microelectrodes is very challenging. This is due to their small size which increases the impedance resulting in poor signal-to-noise ratio (SNR) and distortion. Coating electrodes with Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is a promising approach that was found to reduce their impedance by several orders of magnitude. However, it is also associated with poor adhesion to metals, which severely impacts its stability for chronic usage. In this study, we compared the performances of novel carbon microelectrodes combined with PEDOT:PSS and gold electrodes with PEDOT:PSS coating to Stainless Steel electrodes for the recording and detection of in vivo FRs (mouse hippocampus, kainate model of epilepsy). Results suggest that carbon electrodes allow for better detectability of epileptiform events and, in particular FRs. Perspectives of this work include the design of clinical hybrid (micro-macro) electrodes for the pre-surgical evaluation of patients with Drug-Resistant Epilepsy (DRE) and the design of neural implants for other applications in which chronic recording over long periods of time is required.