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dc.contributor.advisorM. Charles Liberman.en_US
dc.contributor.authorLarsen, Erik, Ph. D. Massachusetts Institute of Technologyen_US
dc.contributor.otherHarvard University--MIT Division of Health Sciences and Technology.en_US
dc.date.accessioned2009-06-30T16:36:49Z
dc.date.available2009-06-30T16:36:49Z
dc.date.copyright2008en_US
dc.date.issued2008en_US
dc.identifier.urihttp://hdl.handle.net/1721.1/45912
dc.descriptionThesis (Ph. D.)--Harvard-MIT Division of Health Sciences and Technology, 2008.en_US
dc.descriptionIncludes bibliographical references (p. 95-101).en_US
dc.description.abstractThis thesis describes results from two projects related to the efferent innervation of the cochlea. First, we investigated peripheral olivocochlear effects of sustained contralateral broadband noise in anesthetized guinea pig. We found evidence of medial olivocochlear (MOC) effects on two timescales: the classic MOC 'fast effect', followed by a gradually increasing suppression, which we call the MOC 'delayed effect'. Delayed suppression typically takes 2-3 minutes to build up, occurs at all frequencies of guinea pig hearing, and suppresses distortion product otoacoustic emissions (DPOAEs), compound action potentials (CAPs), and round window noise. In contrast to the MOC slow effect, which has been reported for sustained shockevoked MOC activity, MOC delayed suppression does not build up in the outer hair cells but is due to a central modulation (enhancement) of MOC responsiveness and can thus be viewed as a gradual increase in the strength of the MOC fast effect. We found that, on average, the magnitude of the delayed suppression is comparable to that of the MOC fast effect, but that there is an overall negative correlation between fast and delayed effect magnitudes. Thus, it may have significant implications for the functional roles of the MOC system, such as protection against acoustic trauma, anti-masking, and dynamic range extension. Second, we investigated the LOC bilateral balancing model, which proposes that the LOC system acts to balance long-term average neural output from both cochleae, which would be important for binaural processing of sounds. For this, we tested various cohorts of mice by repeatedly measuring bilateral auditory brainstem responses (ABR) and "DPOAE growth functions across a wide range of frequencies and levels for periods of about 1-2 months. About halfway through the period, a unilateral reduction in neural output was created, either by acoustic overexposure or conductive impairment. Although the LOC balancing model predicts that the unilateral reduction in neural output should be matched contralaterally, we found no evidence for short-term or long-term efferent-induced contralateral response changes in any of the cohorts, either for DPOAE or ABR metrics.en_US
dc.description.abstract(cont.) In view of these results, a revision of the LOC bilateral balancing model is called for.en_US
dc.description.statementofresponsibilityby Erik Larson.en_US
dc.format.extent101 p.en_US
dc.language.isoengen_US
dc.publisherMassachusetts Institute of Technologyen_US
dc.rightsM.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.en_US
dc.rights.urihttp://dspace.mit.edu/handle/1721.1/7582en_US
dc.subjectHarvard University--MIT Division of Health Sciences and Technology.en_US
dc.titleSlow modulation of cochlear response by the olivocochlear efferent system elicited by sustained noise or threshold elevation in the contralateral earen_US
dc.typeThesisen_US
dc.description.degreePh.D.en_US
dc.contributor.departmentHarvard University--MIT Division of Health Sciences and Technology
dc.identifier.oclc320769241en_US


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