Can Crosstalk Compromise the Recording of High-Frequency Neural Signals?

Two big trends are leading the way to a new generation of thin-film electrocorticography (ECoG) micro electrode arrays (MEAs): miniaturization, which combines higher electrode densities with thinner substrates for conformability purposes; and the pursuit to extend the recording frequency band to 1 kHz and beyond (recording of spikes). When combining these two trends, however, the frequency-dependent phenomenon of crosstalk emerges as a possible setback to the so desired spatial selectivity. In this work, high in vivo coherences at 1 kHz between electrodes with neighboring tracks are reported when using the MuSA (Multi-Species Array) as recording ECoG MEA on rats. These results suggest a high degree of crosstalk between closely routed electrodes, even if placed far apart on the array, and are corroborated by coherence plots of control recordings in vitro in phosphate buffered saline (PBS). As means to estimate the combined leakage resistance and capacitance between the signal lines and the targeted brain tissue, an impedance spatial sweep over the 32 tracks routing the MuSA electrodes is performed in PBS in a two-electrode electrochemical impedance spectroscopy setup. This study should raise awareness of crosstalk as an important aspect to consider when aiming for high-quality, high-density and high-frequency neural recordings.