Long-term analysis of in vivo characteristics of recording electrode using electrochemical impedance spectroscopy

Implanted electrodes are widely used for in vitro and in vivo neural recording; however, the established properties of these electrodes can change over time. Here, we characterize the longterm changes in the electrode surface during in vivo recording and investigate the effect of these changes on visual evoked potentials (VEPs) using electrochemical impedance spectroscopy (EIS) spectra. VEP emulation was simulated on the basis of EIS measurements to identify the factors that contribute to time-dependent changes in the VEP. The VEP measurements revealed a timedependent decrease in the latency for the first negative peak, while the amplitude was stable. EIS measurements revealed a stable impedance. An equivalent circuit analysis confirmed a timedependent increase in solution resistance. However, VEP emulation indicated that the VEP changes were not related to changes in the recording electrode properties, but rather, to changes in vital reactions. Our results suggest that time-dependent VEP measurement requires EIS and emulation analyses to identify changes in the characteristics of the interface between the recording electrode surface and the surrounding tissue and the effects of these changes on electrical recordings.