Recording Quality is Systematically Related to Electrode Impedance.

Extracellular recordings with planar microelectrodes are the gold standard technique for recording the fast action potentials of neurons in the intact brain. The introduction of microfabrication techniques has revolutionized the in vivo recording of neuronal activity and introduced high-density, multi-electrode arrays that increase the spatial resolution of recordings and the number of neurons that can be simultaneously recorded. Despite these innovations, there is still debate about the ideal electrical transfer characteristics of extracellular electrodes. This uncertainty is partly due to the lack of systematic studies comparing electrodes with different characteristics, particularly for chronically implanted arrays over extended time periods. Here we fabricated and tested a high-density, flexible, thin-film array containing four distinct electrode types differing in surface material and surface topology and, thus, impedance. We find that recording quality is strongly related to electrode impedance with signal amplitude and unit yield negatively correlated to impedance. Electrode impedances were stable for the duration of the experiment (up to 12 weeks) and recording quality did not deteriorate. Our findings support the expectation from theory that recording quality will increase as impedance decreases. This article is protected by copyright. All rights reserved.