translation of pedot/parylene c ecog microelectrode arrays for recording auditory cognitive activity in birds
Name: Lorraine Amena Hossain
Grad Year: 2021
Understanding cognitive processing in intact brains is the subject of intense research efforts that aim to resolve individual and network activity of neuronal cells across different layers of the brain. While efforts to record individual cell activity in neural networks are underway, the coordinated activity of networks result in long-range, low frequency oscillations that carry significant cognitive information and is the gold standard for recording cognition from animals and humans. Such activity has been recently recorded with high signal-to-noise ratio from the cortical surface using organic microelectrode arrays that possess superior electrochemical junction characteristics with the brain and is enhanced through conformal coverage of thin parylene C device carrier layers to the brain curvature. We conducted electrocorticography (ECoG) surface recordings in starling birds with simultaneous depth recording of auditory stimulus-evoked responses. In this work, we will describe the fabrication procedure for high-yield PEDOT:PSS microelectrode arrays on parylene C substrates and their ECoG recording capability of cognitive activity from intact brains. The PEDOT devices were fabricated using a conventional surface micromachining procedure in arrays of 5x6 microelectrode channels of 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 deposited from solution and cured in ambient at 140°C for 1 hour. Using adhesive conductive epoxy to bond to ribbon electrical cables, we conducted electrochemical impedance spectroscopy to evaluate the nature of the electrochemical junction, impedances and yield of our process. The microdot impedances were 67.6kΩ±17kΩ with a 96% yield on the best devices. We next implanted the microarrays acutely into the HVC region of the cortex on starlings and optimized the procedure for conformal contact to the brain surface. Upon playing a pre-recording of the bird?s own song, stimulus-related high gamma activity was recorded from the HVC. By altering the auditory stimuli between known and unknown sounds to the bird, different activity was recorded, and the pattern of the activity was largely shaped by the bird?s cognition to the played sounds. The enhanced electrochemical properties of our microelectrodes also enabled the detection of single units from the surface probe. Similar activity has been previously recorded from depth electrodes in the same birds. Therefore, we believe that validation of these microelectrode arrays in decoding cognitive activity from the cortical surface may pave the way for better understanding of information processing in intact brains without brain penetration and recording at depth.
Industry Application Area(s)
Electronics/Photonics | Life Sciences/Medical Devices & Instruments | Materials