The Search for Noise-Induced Cochlear Synaptopathy in Humans: Mission Impossible?


Animal studies demonstrate that noise exposure can permanently damage the synapses between inner hair cells and auditory nerve fibers, even when outer hair cells are intact and there is no clinically relevant permanent threshold shift. Synaptopathy disrupts the afferent connection between the cochlea and the central auditory system and is predicted to impair speech understanding in noisy environments and potentially result in tinnitus and/or hyperacusis. While cochlear synaptopathy has been demonstrated in numerous experimental animal models, synaptopathy can only be confirmed through post-mortem temporal bone analysis, making it difficult to study in living humans. A variety of non-invasive measures have been used to determine whether noise-induced synaptopathy occurs in humans, but the results are conflicting. The overall objective of this article is to synthesize the existing data on the functional impact of noise-induced synaptopathy in the human auditory system. The first section of the article summarizes the studies that provide evidence for and against noise-induced synaptopathy in humans. The second section offers potential explanations for the differing results between studies. The final section outlines suggested methodologies for diagnosing synaptopathy in humans with the aim of improving consistency across studies. ©2019 Elsevier B.V.


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Amplitude modulation, Audiometry, Ear, Auditory pathways, Autopsy, Auditory evoked response, Humans, Hyperacusis, Labyrinth Diseases, Noise, Rodents, Sensitivity and Specificity, Speech, Task Performance and Analysis, Temporal bone, Reproducibility of Results, Tinnitus, Reproducible research

Department of Veterans Affairs, Veterans Health Administration, Rehabilitation Research and Development Service - Award #C2104-W; Australian Government Department of Health, the Hearing Industry Research Consortium, the National Health and Medical Research Council (Grant ID 1063905); Oticon Foundation, Junta de Castilla y León (grant SA023P17), Spanish Ministry of Economy and Competitiveness (grant BFU2015-65376-P); National Institute on Deafness and Other Communication Disorders (1R01DC014088), the Defense Medical Research and Development Program (W81XWH1820014); Medical Research Council (MR/L003589/1 and MR/M023486/1), by the Biotechnology and Biological Sciences Research Council (BB/M007243/1); National Institutes of Health R21DC013172 and 1R56DC016415-01, the Swedish Medical Research Council K2014-99X-22478-01-3, Knut and Alice Wallenberg Foundation (B.C. #KAW2008); The Office of the Assistant Secretary of Defense for Health Affairs, through the Neurosensory and Rehabilitation under Award No. W81XWH-16-1-0032; European Research Council under the Horizon 2020 Research and Innovation Programme (grant agreement No 678120 RobSpear).


©2019 Elsevier B.V.