The purpose of this work is to develop electrode arrays which improve substantially the performance of artificial ears for the deaf. The electrode arrays are placed within the inner ear near the cells of the auditory nerve and are driven with minute electric currents to excite those cells in response to external sound signals. The electrode arrays being developed in our laboratory offer two advantages over arrays currently in use. First, the design of the new arrays will provide at least 60 electrodes whereas today's electrode arrays have only 22 internal electrodes at most. Second, the shape memory materials used in our lab bring the electrodes in proximity to the nerve cells, whereas electrodes in current arrays lie several tenths of a millimeter distant from the nerve cells. During the past year, we placed a test array in the inner ear of a macaque monkey and obtained preliminary results on the behavior of the array. The array was stable during the time of implantation, but the external connector failed to integrate well with the skull of the monkey. We have revised the array and have implanted new connector bases in the skulls of three monkeys. We are experimenting with several fabrication techniques varying the insulation on individual wires, techniques of cleaning electrode sites and electroplating to either increase surface area or provide surfaces that can carry larger excitation currents for a given surface area. Through other funding, we are studying the effects of fibrous capsules on the electrode arrays, and trying to develop techniques to eliminate the capsules. We have begun a series of neurophysiological experiments, which are being done outside of the Primate Center on species other than macaques. These are acute studies that are designed to determine the minimum distance between electrodes to permit independent excitation of small groups of nerve cells.
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