The inner hair cells (IHC) and type-I auditory nerve fibers are thought to provide the only pathway through which auditory information is conveyed to the central auditory system; however, little is known about the deficits in hearing and central auditory function that are associated with damage that is exclusively confined to the IHC/type-I neurons. In the chinchilla, it is possible to selectively destroy a subset of IHC/type-I neurons along the entire length of the cochlea with an anticancer drug. This type of lesion creates a situation in which the central auditory system receives only a small percentage of its normal neural input. What types of hearing deficits are associated with an IHC/type-I lesion? The current proposal will determine directly address this question by measuring five different aspects of hearing: (1) thresholds for hearing long and short duration tones in quiet; this will assess the sensitivity of the system and temporal integration, (2) threshold for detection of tones in broadband noise; this will test the width of the internal auditory filters and the sensitivity of the detector mechanism, (3) masking patterns for narrow band noise; this assess the spread of masking to low and high frequencies, (4) intensity discrimination and frequency discrimination, and (5) modulation thresholds for detection sinusoid ally amplitude modulated noise, a comprehensive measure of temporal resolution. The project will also record the local field potentials from the inferior colliculus and auditory cortex to look at the neural correlates of threshold, increases in intensity, the detection of tones in noise and narrow band noise masking patterns. The changes in hearing function and neural activity will be correlated to the degree of damage to the IHC/type-I neuron. The results of the study could have important implications for developing clinical tests to detect IHC/type-I damage in patients and for understanding auditory neuropathy, a clinical entity thought to involve pathologies of the IHCs or auditory nerve. ? ?
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