Age-related changes in the central nervous system often impair hearing, in particular, speech understanding in noise or other difficult listening situations. This type of age-related central auditory processing disorder is known as central presbycusis. Of note, people with early stage probable Alzheimer dementia (pAD) exhibit signs of poor central auditory processing that are similar to people with central presbycusis except that these signs occur earlier, more prevalently, and to a greater degree than in controls. This suggests that some cases of central presbycusis may be due to incipient Alzheimer dementia and raises the possibility that assessments to detect central auditory processing dysfunction (i.e. central auditory tests) might be useful as a predictor of pAD. The goal of this research is to establish the epidemiologic basis for central auditory testing in the neuropsychological evaluation and in screening for risk and presence of pAD. Before this possibility can be considered, there are many unanswered questions about the association of central auditory dysfunction and pAD. Is the poor speech understanding due to Alzheimer lesions in the auditory pathways, or in the frontal executive control centers that regulate speech processing and attention? Why do most cases of pAD have asymmetric central auditory findings? Is central auditory dysfunction an early manifestation of pAD or a coincident effect of the aging process? Which central auditory measures are most sensitive to early pAD? What proportion of central presbycusis is due to undetected age-related auditory neuropathy secondary to spiral ganglion degeneration? This research application provides a unique opportunity to address these important questions by studying the hearing status of the elderly members of the Adult Change of Thought cohort enrolled in a longitudinal study of aging and dementia in Seattle. By comparing the results of behavioral central auditory tests in the pAD and non-pAD subjects, while controlling for peripheral hearing and neuropsychologic status, we may better understand the effects of aging and dementing disorders upon central auditory function.
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