A Multi-Channel, Flex-Rigid ECoG Microelectrode Array for Visual Cortical Interfacing

Abstract

High-density electrocortical (ECoG) microelectrode arrays are promising signal-acquisition platforms for brain-computer interfaces envisioned, e.g., as high-performance communication solutions for paralyzed persons. We propose a multi-channel microelectrode array capable of recording ECoG field potentials with high spatial resolution. The proposed array is of a 150 mm2 total recording area; it has 124 circular electrodes (100, 300 and 500 μm in diameter) situated on the edges of concentric hexagons (min. 0.8 mm interdistance) and a skull-facing reference electrode (2.5 mm2 surface area). The array is processed as a free-standing device to enable monolithic integration of a rigid interposer, designed for soldering of fine-pitch SMD-connectors on a minimal assembly area. Electrochemical characterization revealed distinct impedance spectral bands for the 100, 300 and 500 μm-type electrodes, and for the array's own reference. Epidural recordings from the primary visual cortex (V1) of an awake Rhesus macaque showed natural electrophysiological signals and clear responses to standard visual stimulation. The ECoG electrodes of larger surface area recorded signals with greater spectral power in the gamma band, while the skull-facing reference electrode provided higher average gamma power spectral density (γPSD) than the common average referencing technique.

Annealing Effects of Parylene-Caulked Polydimethylsiloxane as a Substrate of Electrodes

“…In addition, the electrode impedance based on both substrates converged to similar values after 200 days. The measured impedance magnitudes were comparable with those of other surface-type electrodes [37,38,39,40]. Annealing turned out to contribute to the increase in the electrode impedance without a reduction of the electrode areas.…”

Silicon-Integrated High-Density Electrocortical Interfaces

“…(d) Flexible 252-channel ECoG electrode array on a thin polyimide foil substrate [24]. (e) ECoG electrode array with 124 circular electrodes with three different diameters [25]. (f) Parylene-coated metal tracks and electrodes within a silicone rubber substrate [26].…”

Wafer‐Scale Fabrication of Conducting Polymer Hydrogels for Microelectrodes and Flexible Bioelectronics

“…Nevertheless, from our experience of electrodeposition of PEDOT/PSS having all electrodes short‐circuited on the wafer, we see no reason why not this step could also be performed on wafer‐scale in the future, especially as the localized charge provided by the hydrogel would prevent growth on any other surface. The deposition of PEDOT was here demonstrated with electrodes of 35 and 500 µm in diameter, which were chosen to represent two common size scales for intracortical and epicortical electrodes, respectively . The described coating procedures resulted in homogenous coatings with comparable outcome between the individual PI probes and electrode sizes as evidenced from a CV analysis of electrodes located at different positions on the wafer.…”