Validation of high density electrode arrays for cochlear implants: a computational and structural approach
Falcone, Jessica Dominique
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Creating high resolution, or high-density, electrode arrays may be the key for improving cochlear implant users' speech perception in noise, comprehension of lexical languages, and music appreciation. Contemporary electrode arrays use multipolar stimulation techniques such as current steering (shifting the spread of neural excitation in between two physical electrodes) and current focusing (narrowing of the neural spread of excitation) to increase resolution and more specifically target the neural population. Another approach to increasing resolution incorporates microelectromechanical systems (MEMS) fabrication to create a thin film microelectrode (TFM) array with a series of high density electrodes. Validating the benefits of high density electrode arrays requires a systems-level approach. This hypothesis will be tested computationally via cochlea and auditory nerve simulations, and in vitro studies will provide structural proof-of-concept. By employing Rattay's activating function and entering it into Litvak's neural probability model, a first order estimation model was obtained of the auditory nerve's response to electrical stimulation. Two different stimulation scenarios were evaluated: current steering vs. a high density electrode and current focusing of contemporary electrodes vs. current focusing of high density electrodes. The results revealed that a high density electrode is more localized than current steering and requires less current. A second order estimation model was also created COMSOL, which provided the resulting potential and current flow when the electrodes were electrically stimulated. The structural tests were conducted to provide a proof of concept for the TFM arrays' ability to contour to the shape of the cochlea. The TFM arrays were integrated with a standard insertion platform (IP). In vitro tests were performed on human cadaver cochleae using the TFM/IP devices. Fluoroscopic images recorded the insertion, and post analysis 3D CT scans and histology were conducted on the specimens. Only three of the ten implanted TFM/IPs suffered severe delamination. This statistic for scala vestibuli excursion is not an outlier when compared to previous data recorded for contemporary cochlear electrode arrays.