title: Tinnitus with a normal audiogram: Relation to noise exposure but no evidence for cochlear synaptopathy.
abstract: In rodents, exposure to high-level noise can destroy synapses between inner hair cells and auditory nerve fibers, without causing hair cell loss or permanent threshold elevation. Such "cochlear synaptopathy" is associated with amplitude reductions in wave I of the auditory brainstem response (ABR) at moderate-to-high sound levels. Similar ABR results have been reported in humans with tinnitus and normal audiometric thresholds, leading to the suggestion that tinnitus in these cases might be a consequence of synaptopathy. However, the ABR is an indirect measure of synaptopathy and it is unclear whether the results in humans reflect the same mechanisms demonstrated in rodents. Measures of noise exposure were not obtained in the human studies, and high frequency audiometric loss may have impacted ABR amplitudes. To clarify the role of cochlear synaptopathy in tinnitus with a normal audiogram, we recorded ABRs, envelope following responses (EFRs), and noise exposure histories in young adults with tinnitus and matched controls. Tinnitus was associated with significantly greater lifetime noise exposure, despite close matching for age, sex, and audiometric thresholds up to 14 kHz. However, tinnitus was not associated with reduced ABR wave I amplitude, nor with significant effects on EFR measures of synaptopathy. These electrophysiological measures were also uncorrelated with lifetime noise exposure, providing no evidence of noise-induced synaptopathy in this cohort, despite a wide range of exposures. In young adults with normal audiograms, tinnitus may be related not to cochlear synaptopathy but to other effects of noise exposure.
authors.affiliation: Manchester Centre for Audiology and Deafness, University of Manchester, Manchester Academic Health Science Centre, UK. Electronic address: hannah.guest@manchester.ac.uk.
authors.forename: Hannah
authors.initials: H
authors.lastname: Guest
authors.affiliation: Manchester Centre for Audiology and Deafness, University of Manchester, Manchester Academic Health Science Centre, UK; Central Manchester University Hospitals NHS Foundation Trust, Manchester, UK.
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Munro
authors.affiliation: Manchester Centre for Audiology and Deafness, University of Manchester, Manchester Academic Health Science Centre, UK.
authors.forename: Garreth
authors.initials: G
authors.lastname: Prendergast
authors.affiliation: Audiology Department, James Cook University Hospital, South Tees Hospitals NHS Foundation Trust, Middlesbrough, UK.
authors.forename: Simon
authors.initials: S
authors.lastname: Howe
authors.affiliation: Manchester Centre for Audiology and Deafness, University of Manchester, Manchester Academic Health Science Centre, UK; Department of Psychology, Lancaster University, Lancaster, UK.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Plack
mesh_terms: D000161:Acoustic Stimulation; D000328:Adult; D001309:Auditory Threshold; D016022:Case-Control Studies; D003051:Cochlea / Q000503:physiopathology*; D004569:Electroencephalography; D016057:Evoked Potentials, Auditory, Brain Stem; D005260:Female; D006309:Hearing; D006317:Hearing Loss, Noise-Induced / Q000175:diagnosis / Q000503:physiopathology* / Q000523:psychology; D006801:Humans; D008297:Male; D009622:Noise / Q000009:adverse effects*; D011571:Psychoacoustics; D012307:Risk Factors; D009435:Synaptic Transmission; D014012:Tinnitus / Q000175:diagnosis / Q000503:physiopathology* / Q000523:psychology; D055815:Young Adult
keywords: Auditory brainstem response; Cochlear synaptopathy; Envelope following response; Hidden hearing loss; Noise-induced hearing loss; Tinnitus