Hearing deficits are the third leading cause of disability in the aged. Over half of all people in the US over seventy suffer some form of age-related hearing deficits. This is a ubiquitous problem with many sources, and the peripheral contributions to age-related deficits, particularly high frequency hearing loss, have been explored and have revealed several important features of these disorders. However, there remains relatively little understood about the consequences of age-related hearing loss and normal aging on central auditory structures, particularly the neocortex, and how age-related changes in either anatomical or physiological processes in central structures give rise to perceptual deficits. Our lack of understanding of these central effects is due in large part to the lack of an effective animal model that (1) shares many organizational features of auditory cortex with humans, (2) has a reasonably long life span such that age-related hearing deficits progress over the course of several years as in the human, and (3) are not prohibitively expensive. The goals of this proposal are to fill this gap by correlating hearing deficits related to either age or hearing loss with single neuron activity in core and belt areas of auditory cortex as well as the perceptual abilities and the cochlear morphology of the same individuals. Experimental groups will include young animals with no hearing loss, young animals with hearing loss, geriatric animals with minimal hearing loss and geriatric animals with hearing loss. Animals will be trained on spatial and temporal discrimination tasks and cortical activity will be directly correlated with this behavioral performance, hearing thresholds, and cochlear morphology. Comparisons between neurons in different animals, as well as in auditory cortical fields that have been reorganized due to the high frequency hearing loss, will be compared to determine which aspects of auditory information processing are most susceptible to aging and age-related hearing loss. The results of this study are a critical step in the development of new remedial treatments and therapies, as well as in hearing aid design, for individuals suffering from age-related hearing deficits.
By investigating age-related hearing deficits at the level of the cerebral cortex and correlating these findings with perceptual deficits, pure tone audiograms, and cochlear morphology we will be breaking new ground in understanding this ubiquitous disability. Knowledge of the peripheral and central dysfunctions leading to these deficits is absolutely critical in developing new remedial therapies and treatments.
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