Effects of Remaining Hair Cells on Cochlear Implant Function

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Principal Investigator	Affiliation	Contract Number	Link
Paul Abbas, Ph.D.	University of Iowa	N01-DC9-21	U of Iowa

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Project Title: Effects of Remaining Hair Cells on Cochlear Implant Function, June 1998

1. Background

Research and development on auditory prostheses for deaf individuals is supported by the National Institute on Deafness and Other Communication Disorders (NIDCD). As more people with some remaining hearing receive cochlear implants and as insertion trauma is reduced during implantation, there will be more cases of implanted individuals with some surviving hair cells. There is reason to believe that these hair cells could have both beneficial and detrimental effects on the function of cochlear implants.

This research project, to be performed in animals with cochlear implants, will determine the relationship between hair cell survival and cochlear implant function. It should answer the following questions:

1. Does the presence of hair cells help to reduce the synchronous firing of auditory nerve fibers by electrical stimulation and can this effect be optimized to make their firing more stochastic?

2. What role does acoustic activation of remaining hair cells have on the patterns of activation and survival of remaining auditory nerve fibers?

3. If remaining hair cells also have potentially negative effects on cochlear implant function, how can these effects be reduced or eliminated without affecting positive attributes?

Note to offerors: This solicitation is for new research and has not previously been supported by NIDCD. A bibliography of publications resulting from related research contracts is available on the Neural Prosthesis Program Homepage: http://www.ninds.nih.gov/npp

2. Objectives

The objectives of this contract are to understand the effects of remaining hair cells on the activation of auditory nerve fibers by cochlear electrodes and to control these effects for optimum cochlear implant function.

3. Work to be Performed

Independently, and not as an agent of the Government, the Contractor shall develop an animal model of severely hearing impaired, but not totally deaf, humans and investigate the effects of the remaining hair cells on the remaining auditory system during activation by cochlear implants. Specifically, the Contractor shall:

A. Develop an animal model, or adapt an existing model, of cochlear degeneration resembling humans who have both adult onset, severe, but not total, hearing impairment and have been implanted with a cochlear electrode array.

1. Utilize in-vivo tests to document a substantial, but not total, loss of hair cells and the survival of a significant number of auditory nerve fibers.

2. When developing this model, determine the expected pattern(s) of survival of the remaining hair cells and auditory nerve fibers and any other cochlear lesions with histopathological examination.

B. Develop another animal model, or adapt an existing model, that has all of the hair cells destroyed in one ear and the other ear normal at the time of cochlear electrode implantation.

C. Utilize the animal models to determine whether the presence of hair cells can affect the firing of auditory nerve cells that are directly activated by a cochlear electrode. If the hair cells affect firing:

1. Determine if they can be utilized to vary the activation patterns of auditory nerve fibers and in particular, if they can effect a reduction in the electrical stimulus induced synchronous activation of auditory nerve fibers that becomes increasingly pronounced with lower stimulus rates.

2. Determine whether effects are modulated by acoustic input to the ear at sound levels that should stimulate hair cells even in the presence of a cochlear implant in the same cochlea.

a. If modulation does occur, study the relationship between the acoustic input and any increase in stochastic response.

3. Determine whether the presence of hair cells might have negative effects on cochlear implant function.

D. In a subset of the animals which were not totally deafened, after completion of the initial neurophysiological studies, totally deafen the animals and note differences, if any, in the cochlear implant induced activation patterns.

1. Since deafening this group of animals will prevent the histopathological determination of the anatomical status of the cochlea prior to deafening, try to develop neurophysiological tests of the status of hair cell and auditory nerve fiber survival just prior to total deafening.

E. In the animals studied neurophysiologically, utilize histopathological techniques to examine the positions of the electrodes in the cochleas, the type and location of any surviving hair cells and supporting cells, the survival of auditory nerve fibers, and any other damage that might have occurred to the cochlear tissues.

F. At the conclusion of the animal studies, suggest ways that the results might be utilized to improve cochlear implant function in severely hearing impaired humans.