Design, Characterization and In Vivo Application of Multi-Conductive Layer Organic Electrocorticography Probes

Biocompatible and plastic neural interface devices allow for minimally invasive recording of brain activity. Increasing electrode density on such devices is essential for high resolution neural recordings. Superimposing conductive leads on devices can help multiplying the number of recording sites while keeping probes width small and suitable for implantation. However, because of leads’ vertical proximity, this can create capacitive coupling (CC) between overlapping channels, which leads to crosstalk. In our study, we present a thorough investigation of CC phenomenon in multi gold layer thin-film MEAs with a Parylene C (PaC) insulation layer between superimposed leads. We also propose a guideline on the design, fabrication and characterization of such type of neural interface devices for high spatial resolution recording. Our results demonstrate that the capacitance created through CC between superimposed tracks decreases non-linearly then linearly with insulation thickness. Moreover, CC creates a high pass filter between superimposed leads, with maximum gain and cutoff frequency depending not only on device geometry but also on the recording equipment. We identified that there is an optimal PaC insulation thickness that leads to a drastic reduction of CC between superimposed gold channels, while not significantly increasing the overall device thickness. Finally, we show that double gold layer electrocorticography probes with this optimal insulation thickness exhibit similar performances <i>in vivo</i> when compared to single layer devices. This confirms that these probes are adequate for high-quality neural recordings.