Translation of PEDOT/Parylene C ECoG microelectrode arrays for recording stimulus driven action potentials in songbirds

L. HOSSAIN; E. ARNEODO; M. GANJI; N. ROGERS; T. GENTNER; V. GILJA; S. DAYEH

San Diego

Conferencia; SfN 2018; 2018

Society for Neuroscience

Understanding cognitive processing in intact brains is the subject of intense research efforts to resolve stimulus-evoked activity of individual and networks of neurons across different cortical layers. Traditionally, single unit activity is conveniently recorded with penetrating depth electrodes. But these electrodes cause damage to natural structure and connection in the brain tissue. Recording single unit activity from the cortical surface has been demonstrated recently with low impedance PEDOT:PSS microelectrodes built on thin flexible substrates. Here, we build similar devices with ?through? vias in between the microelectrode contacts and insert depth electrodes to validate and correlate surface recorded activity with activity at underlying cortical layers and demonstrate stimulus-evoked single unit activity at the cortical surface in songbird experiments.The PEDOT devices were fabricated using a conventional surface micromachining procedure in arrays of 5x6 microelectrodes with 20μm diameter and 200μm center-to-center spacing. The metal lines were embedded in ~2.9μm parylene C on both sides, and the PEDOT:PSS was spun-cast from solution and cured in ambient at 140°C for 1 hour. Electrochemical impedance spectroscopy was used to evaluate the properties of the electrochemical junction and yield of our process. The microelectrode impedance magnitudes were 67.6kΩ±17kΩ at 1kHz, with a 96% yield on the best devices. We implanted the microarrays acutely into the HVC region of the cortex on starlings (n=6) and optimized the procedure for conformal contact to the brain surface. Recordings were on both male and female starlings with Testosterone administered 2-5 weeks before recording. Upon playing a pre-recording of the bird?s own song, stimulus-evoked high gamma activity was observed from the HVC. By altering the auditory stimuli, distinct activity was recorded that is highly correlated to the stimuli when the song was known to the bird and less correlated for the unknown stimuli. The enhanced electrochemical properties of our microelectrodes also enabled the detection of single units from the surface. Like the LFP, these surface spikes were evoked by the auditory stimuli of the bird?s own song. These characteristics match the spiking patterns previously recorded from depth electrodes in the same birds. Therefore, we believe that validation of these microelectrode arrays in decoding stimulus-evoked activity from the surface may pave the way for better understanding of information processing in superficial layers in intact brains and without penetrating the brain to record from deeper layers.