Table of Contents Author Guidelines Submit a Manuscript
BioMed Research International
Volume 2018 (2018), Article ID 6280969, 12 pages
https://doi.org/10.1155/2018/6280969
Research Article

Transient Abnormalities in Masking Tuning Curve in Early Progressive Hearing Loss Mouse Model

1Neurosensory Biophysics, INSERM UMR 1107, Clermont Auvergne University, Clermont-Ferrand, France
2Speech Therapy and Audiology Department, Federal University of Minas Gerais, Belo Horizonte, MG, Brazil
3Cellular Health Imaging Center, Clermont Auvergne University, Clermont-Ferrand, France

Correspondence should be addressed to Fabrice Giraudet; rf.acu@teduarig.ecirbaf

Received 10 October 2017; Accepted 26 December 2017; Published 13 February 2018

Academic Editor: Jeong-Han Lee

Copyright © 2018 Marion Souchal et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Damage to cochlear outer hair cells (OHCs) usually affects frequency selectivity in proportion to hearing threshold increase. However, the current clinical heuristics that attributes poor hearing performance despite near-normal auditory sensitivity to auditory neuropathy or “hidden” synaptopathy overlooks possible underlying OHC impairment. Here, we document the part played by OHCs in influencing suprathreshold auditory performance in the presence of noise in a mouse model of progressive hair cell degeneration, the CD1 strain, at postnatal day 18–30 stages when high-frequency auditory thresholds remained near-normal. Nonetheless, total loss of high-frequency distortion product otoacoustic emissions pointed to nonfunctioning basal OHCs. This “discordant profile” came with a huge low-frequency shift of masking tuning curves that plot the level of interfering sound necessary to mask the response to a probe tone, against interfering frequency. Histology revealed intense OHC hair bundle abnormalities in the basal cochlea uncharacteristically associated with OHC survival and preserved coupling with the tectorial membrane. This pattern dismisses the superficial diagnosis of “hidden” neuropathy while underpinning a disorganization of cochlear frequency mapping with optimistic high-frequency auditory thresholds perhaps because responses to high frequencies are apically shifted. The audiometric advantage of frequency transposition is offset by enhanced masking by low-frequency sounds, a finding essential for guiding rehabilitation.