An unusually powerful mode of low-frequency sound interference due to defective hair bundles of the auditory outer hair cells

K Kamiya, V Michel, F Giraudet… - Proceedings of the …, 2014 - National Acad Sciences
K Kamiya, V Michel, F Giraudet, B Riederer, I Foucher, S Papal, I Perfettini, S Le Gal…
Proceedings of the National Academy of Sciences, 2014National Acad Sciences
A detrimental perceptive consequence of damaged auditory sensory hair cells consists in a
pronounced masking effect exerted by low-frequency sounds, thought to occur when
auditory threshold elevation substantially exceeds 40 dB. Here, we identified the
submembrane scaffold protein Nherf1 as a hair-bundle component of the differentiating
outer hair cells (OHCs). Nherf1−/− mice displayed OHC hair-bundle shape anomalies in the
mid and basal cochlea, normally tuned to mid-and high-frequency tones, and mild (22–35 …
A detrimental perceptive consequence of damaged auditory sensory hair cells consists in a pronounced masking effect exerted by low-frequency sounds, thought to occur when auditory threshold elevation substantially exceeds 40 dB. Here, we identified the submembrane scaffold protein Nherf1 as a hair-bundle component of the differentiating outer hair cells (OHCs). Nherf1−/− mice displayed OHC hair-bundle shape anomalies in the mid and basal cochlea, normally tuned to mid- and high-frequency tones, and mild (22–35 dB) hearing-threshold elevations restricted to midhigh sound frequencies. This mild decrease in hearing sensitivity was, however, discordant with almost nonresponding OHCs at the cochlear base as assessed by distortion-product otoacoustic emissions and cochlear microphonic potentials. Moreover, unlike wild-type mice, responses of Nherf1−/− mice to high-frequency (20–40 kHz) test tones were not masked by tones of neighboring frequencies. Instead, efficient maskers were characterized by their frequencies up to two octaves below the probe-tone frequency, unusually low intensities up to 25 dB below probe-tone level, and growth-of-masker slope (2.2 dB/dB) reflecting their compressive amplification. Together, these properties do not fit the current acknowledged features of a hypersensitivity of the basal cochlea to lower frequencies, but rather suggest a previously unidentified mechanism. Low-frequency maskers, we propose, may interact within the unaffected cochlear apical region with midhigh frequency sounds propagated there via a mode possibly using the persistent contact of misshaped OHC hair bundles with the tectorial membrane. Our findings thus reveal a source of misleading interpretations of hearing thresholds and of hypervulnerability to low-frequency sound interference.
National Acad Sciences