The Effects of Hair-Cell Specific Dysfunction on Neural Coding In the Auditory Periphery

David R Axe, Purdue University

Abstract

Sensorineural hearing loss (SNHL) is a disease that disrupts the quality of life of millions of people around the world. The term SNHL is in many ways a catchall for several conditions that can result from a wide array of sources, including noise over-exposure, chemical ototoxicity, and aging. Moreover, the specific pattern of degradation can vary dramatically from patient to patient. Two patients presenting similar audiograms can have significantly different ability in speech intelligibility. Both patients may be diagnosed with SNHL, but their cochlea where the damage has occurred remains in many ways a “black box” in terms of diagnostic specificity. This common clinical outcome illustrates the need for additional diagnostic measures, which will require a more detailed understanding of the variety of mechanistic changes that can occur following SNHL. The goal of this work was to investigate several underlying mechanisms of SNHL by selectively perturbing individual components of the peripheral auditory system, specifically the inner and outer hair-cells of the cochlea. This was accomplished by measuring both invasive single-unit and non-invasive evoked neural responses in chinchillas that were administered specific ototoxic drugs. Responses were measured to stimuli ranging from simple tones to more complex sounds, including amplitude- and frequency-modulated tones and broadband noise, which represent fundamental acoustic features of speech and music in real-world environments. This experimental approach made it possible to measure the effects of damage to each cell type on peripheral neural processing in isolation, i.e., without the confounding interactions of damage to other peripheral components that often occurs with noise over-exposure. Inner-hair-cell dysfunction produced subtle or no effects on common threshold measurements, but perceptually relevant effects were predicted for suprathreshold sounds. Frequency-modulated tones may be effective stimuli for inner-hair-cell diagnostics. Changes in distortion-product otoacoustic emissions were predictive of several physiological effects of outer-hair-cell dysfunction.

Degree

Ph.D.

Advisors

Heinz, Purdue University.

Subject Area

Audiology|Neurosciences|Biomedical engineering|Physiology

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