Chronic tinnitus is a prevalent hearing disorder, and yet no successful treatments or objective diagnostic tests are currently available. The aim of this study was to investigate the relationship between the presence of tinnitus and the strength of the middle-ear-muscle reflex (MEMR) in humans with normal and near-normal hearing. Clicks were used as test stimuli to obtain a wideband measure of the effect of reflex activation on ear-canal sound pressure. The reflex was elicited using a contralateral broadband noise. The results show that the reflex strength is significantly reduced in individuals with noise-induced continuous tinnitus and normal or near-normal audiometric thresholds compared with no-tinnitus controls. Due to a shallower growth of the reflex strength in the tinnitus group, the difference between the two groups increased with increasing elicitor level. No significant difference in the effect of tinnitus on the strength of the middle-ear muscle reflex was found between males and females. The weaker reflex could not be accounted for by differences in audiometric hearing thresholds between the tinnitus and control groups. Similarity between our findings in humans and the findings of a reduced middle-ear muscle reflex in noise-exposed animals suggests that noise-induced tinnitus in individuals with clinically normal hearing may be a consequence of cochlear synaptopathy, a loss of synaptic connections between inner hair cells (IHCs) in the cochlea and auditory-nerve (AN) fibers that has been termed hidden hearing loss.
Bibliographical noteFunding Information:
This work was supported by National Institutes of Health Grants R01 DC015987 (to M.W.) and R01 DC012262 (to A.J.O.). Correspondence should be addressed to Magdalena Wojtczak, Department of Psychology, N218 Elliott Hall, 75 East River Road, Minneapolis, MN 55455, E-mail: firstname.lastname@example.org. DOI:http://dx.doi.org/10.1523/ENEURO.0363-17.2017 Copyright © 2017 Wojtczak et al. This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license, which permits unrestricted use, distribution and reproduction in any medium provided that the original work is properly attributed.
- Cochlear synaptopathy
- Hidden hearing loss
- Middle-ear-muscle reflex
- Noise exposure
- Stapedial reflex