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      Age-Related Hearing Loss in Rhesus Monkeys Is Correlated with Cochlear Histopathologies

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          Abstract

          Audiometric hearing deficits are a common symptom of age-related hearing loss (ARHL), as are specific histopathological changes in the cochlea; however, very little data have been collected in non-human primates. To examine this relationship further, we collected auditory brainstem responses (ABRs) from rhesus monkeys spanning in age from 10 to 35 years old, and examined four different morphological features of their cochleae. We found significant correlations between ABR thresholds and the loss of outer hair cells and spiral ganglion cells, but not with the loss of inner hair cells or a reduced thickness of the stria vascularis. The strongest correlation with ABR thresholds was the number of different pathologies present. These findings show that while aged rhesus monkeys experience audiometric hearing deficits similar to that seen in humans, they are not correlated with a single peripheral deficit, but instead with a number of different underlying cochlear histopathologies, indicating that similar histopathologies may exist in geriatric humans as well.

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          Subdivisions of auditory cortex and processing streams in primates.

          The auditory system of monkeys includes a large number of interconnected subcortical nuclei and cortical areas. At subcortical levels, the structural components of the auditory system of monkeys resemble those of nonprimates, but the organization at cortical levels is different. In monkeys, the ventral nucleus of the medial geniculate complex projects in parallel to a core of three primary-like auditory areas, AI, R, and RT, constituting the first stage of cortical processing. These areas interconnect and project to the homotopic and other locations in the opposite cerebral hemisphere and to a surrounding array of eight proposed belt areas as a second stage of cortical processing. The belt areas in turn project in overlapping patterns to a lateral parabelt region with at least rostral and caudal subdivisions as a third stage of cortical processing. The divisions of the parabelt distribute to adjoining auditory and multimodal regions of the temporal lobe and to four functionally distinct regions of the frontal lobe. Histochemically, chimpanzees and humans have an auditory core that closely resembles that of monkeys. The challenge for future researchers is to understand how this complex system in monkeys analyzes and utilizes auditory information.
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            Uses and abuses of hearing loss classification.

            P. Clark (1981)
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              Speech recognition in noise and presbycusis: relations to possible neural mechanisms.

              This study is part of ongoing efforts to characterize and determine the neural bases of presbycusis. These efforts utilize humans and animals in sets of overlapping hypotheses and experiments. Here, 50 young adult and elderly subjects, with normal audiometric thresholds or high-frequency hearing loss, were presented three types of linguistic materials at suprathreshold levels to determine speech recognition performance in noise. The study sought to determine how peripheral and central auditory system dysfunctions might be implicated in the speech recognition problems of elderly humans. There were four main findings. (1) Peripheral auditory nervous system pathologies, manifested as reduced sensitivity for speech-frequency pure tones and speech materials, contribute to elevated speech reception thresholds in quiet, and to reduced speech recognition in noise. (2) Good cognitive ability was demonstrated in the old subjects who took advantage of supportive context as well or better than young subjects, strongly indicating that the cortical portions of the speech/language nervous system did not account for the speech understanding dysfunctions of the old subjects. (3) When audibility and cognitive functioning were not affected, the demonstrated speech-recognition in-noise dysfunction remained in old subjects. This implicates auditory brainstem or auditory cortex temporal-resolution dysfunctions in accounting for the observed differences in speech processing. (4) Performance differences between young and elderly subjects with elevated thresholds illustrate the effects of age plus hearing loss and thereby implicate both peripheral and central dysfunctions in presbycusics. This is because the differences in performance between young and elderly subjects with normal peripheral sensitivity identified a central auditory dysfunction.
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                Author and article information

                Contributors
                Role: Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, USA )
                1932-6203
                2013
                4 February 2013
                : 8
                : 2
                : e55092
                Affiliations
                [1 ]Evelyn F. McKnight Brain Institute and ARL Division of Neural Systems, Memory and Aging, University of Arizona, Tucson, Arizona, United States of America
                [2 ]Department of Otolaryngology, University of California Davis, Davis, California, United States of America
                [3 ]Center for Neuroscience, University of California Davis, Davis, California, United States of America
                [4 ]Department of Neurobiology, Physiology and Behavior, University of California Davis, Davis, California, United States of America
                UNLV, United States of America
                Author notes

                Competing Interests: The authors have declared that no competing interests exist.

                Conceived and designed the experiments: JRE GHR. Performed the experiments: JRE ST GHR. Analyzed the data: JRE ST GHR. Contributed reagents/materials/analysis tools: JRE ST GHR. Wrote the paper: JRE GHR.

                Article
                PONE-D-12-27320
                10.1371/journal.pone.0055092
                3563598
                23390514
                4f01ad5c-326f-4caa-b613-29ec38b30438
                Copyright @ 2013

                This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 5 September 2012
                : 21 December 2012
                Page count
                Pages: 13
                Funding
                Funded by National Institute on Aging (NIA) R21AG024372, R01AG034137 (GHR), and National Institute on Deafness and Other Communication Disorders (NIDCD) T32DC008072 (JRE) and R01DC008649 (ST). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
                Categories
                Research Article
                Biology
                Anatomy and Physiology
                Neurological System
                Neuroanatomy
                Physiological Processes
                Aging
                Model Organisms
                Animal Models
                Neuroscience
                Sensory Perception
                Medicine
                Anatomy and Physiology
                Neurological System
                Neuroanatomy
                Physiological Processes
                Aging
                Mental Health
                Psychology
                Sensory Perception
                Otorhinolaryngology
                Otology
                Hearing Disorders

                Uncategorized
                Uncategorized

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