The sense of hearing is initialized in the inner ear by signal transduction; i.e., the transformation of sound to electrical signals. Normal cochlear function relies on the integrity and functionality of the hair cells that act as mechano-electric transducers. Cochlear transduction is vulnerable to structural and metabolic alterations in the inner ear that consequently lead to hearing loss; therefore, techniques that can assess cochlear transduction would be a desirable clinical tool to evaluate cochlear function. The long-term goal of the proposed research is to characterize cochlear transduction in cochlear disorders and, in turn, to develop a diagnostic tool that can no invasively distinguish cochlear hearing losses. The transduction processes in the hair cells produce sound or acoustic emissions that are measurable in the ear canal. Evoked by two-tone stimuli, the distortion product otoacoustic emissions (DPOAEs) are generated from the nonlinearity in cochlear transduction. Recently, we have developed a technique to derive a nonlinear transducer function of the inner ear from low-frequency modulation of DPOAEs. The modulation patterns of the DPOAEs provide physiologic indices of cochlear transduction. To continue our research towards the long-term goal, three studies, two in animals and one in the humans, are proposed. In the animal studies, the specific aim is to determine the sensitivity and specificity of the transducer function and the associated indices in detecting cochlear pathologies. The sensitivity of the transduction indices will be tested in animals with moderate temporary hearing loss induced by exposures to pure tones. The specificity will be evaluated by differences in the change of transducer functions obtained from animals with hearing losses produced by different ototoxic drugs.
The specific aim of the human study is to obtain normative values, the variability and reliability of the cochlear transduction indices derived from the low-frequency modulation of DPOAEs. Successful completion of the proposed research will provide a solid base for future development of a clinical tool that is helpful in the early identification of cochlear disorders, a critical practice in otology and audiology for treatment and hearing preservation. ? ?
