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Cochlear synaptopathy and tinnitus in veterans (Bramhall et al., 2023)

posted on 2023-10-27, 14:17 authored by Naomi F. Bramhall, Sarah M. Theodoroff, Garnett P. McMillan, Sean D. Kampel, Brad N. Buran

Purpose: Animal models and human temporal bones indicate that noise exposure is a risk factor for cochlear synaptopathy, a possible etiology of tinnitus. Veterans are exposed to high levels of noise during military service. Therefore, synaptopathy may explain the high rates of noise-induced tinnitus among Veterans. Although synaptopathy cannot be directly evaluated in living humans, animal models indicate that several physiological measures are sensitive to synapse loss, including the auditory brainstem response (ABR), the middle ear muscle reflex (MEMR), and the envelope following response (EFR). The purpose of this study was to determine whether tinnitus is associated with reductions in physiological correlates of synaptopathy that parallel animal studies.

Method: Participants with normal audiograms were grouped according to Veteran status and tinnitus report (Veterans with tinnitus, Veterans without tinnitus, and non-Veteran controls). The effects of being a Veteran with tinnitus on ABR, MEMR, and EFR measurements were independently modeled using Bayesian regression analysis.

Results: Modeled point estimates of MEMR and EFR magnitude showed reductions for Veterans with tinnitus compared with non-Veterans, with the most evident reduction observed for the EFR. Two different approaches were used to provide context for the Veteran tinnitus effect on the EFR by comparing to agerelated reductions in EFR magnitude and synapse numbers observed in previous studies. These analyses suggested that EFR magnitude/synapse counts were reduced in Veterans with tinnitus by roughly the same amount as over 20 years of aging.

Conclusion: These findings suggest that cochlear synaptopathy may contribute to tinnitus perception in noise-exposed Veterans.

Supplemental Material S1. Modeled population contrasts in mean auditory brainstem response wave I amplitude.

Supplemental Material S2. Modeled population contrasts in mean middle ear muscle reflex magnitude.

Supplemental Material S3. Modeled population contrasts in mean envelope following response magnitude.

Bramhall, N. F., Theodoroff, S. M., McMillan, G. P., Kampel, S. D., & Buran, B. N. (2023). Associations between physiological correlates of cochlear synaptopathy and tinnitus in a veteran population. Journal of Speech, Language, and Hearing Research. Advance online publication.


This work was supported by Department of Veterans Affairs (VA), Veterans Health Administration, Rehabilitation Research and Development Service (RR&D) Award C2104-W/IK2 RX002104 (to N.F.B.) and by resources and facilities at the VA RR&D National Center for Rehabilitative Auditory Research (NCRAR; Center Award C2361C/I50 RX002361) at the VA Portland Health Care System in Portland, Oregon. Research audiologist support was also provided by the Department of Defense Hearing Center of Excellence and zCore Business Solutions, Inc. The opinions and assertions presented are private views of the authors and are not to be construed as official or as necessarily reflecting the views of the VA or the Department of Defense.