One solution to the problem of sensorineural (inner ear) deafness is to bypass the damaged hair cells of the inner ear and directly stimulate the remaining auditory nerve fibers electrically using the cochlear prosthesis. The processor for the cochlear prosthesis consists of a signal analyzer and an electrical stimulator. The analyzer determines the information to be sent over a specific implant channel to the nervous system and the stimulator determines the electrical stimulus used to transfer that information. Most prostheses use the analyzer output as the electrical stimulus and as a result, much of the waveform information from the analyzer is lost. This project proposes to remedy this problem by developing and testing a novel stimulus strategy, based on controlling the auditory nerve neural population in a digital fashion which will encode the output waveform information from the analyzer. The neural population in the vicinity of a stimulating electrode is theoretically divided by calculated equal potential contours into small discrete subpopulations. The electrical stimulus amplitude that will stimulate the desired number of neural subpopulation groups, proportional to the amplitude of the analyzer's output, is then determined and produced. This process is repeated for each pulse of the 5 KHz electrical stimulus, producing current levels that will stimulate the number of neural digital building blocks that is proportional to the analyzer's waveform. This essentially performs an analog to digital conversion of the analyzer's output. This complex stimulus strategy requires digital computer technology. It requires the development of a three dimensional electrical field/multineural model which will track the refractory status and response of each of these neural digital building blocks. The effectiveness of this strategy will be tested in a three dimensional electrical field/multineural model of the cochlea and through single auditory neuron studies in implanted squirrel monkeys.
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