Outer hair cells (OHCs) in the mammalian ear exhibit electromotility, electrically driven somatic length changes that are thought to mechanically amplify sound-evoked vibrations. For this amplification to work, OHCs must respond to sounds on a cycle-by-cycle basis even at frequencies that exceed the low-pass corner frequency of their cell membranes. Using in vivo optical vibrometry we tested this theory by measuring sound-evoked motility in the 13-25 kHz region of the gerbil cochlea. OHC vibrations were strongly rectified, and motility exhibited first-order low-pass characteristics with corner frequencies around 3 kHz- more than 2.5 octaves below the frequencies the OHCs are expected to amplify. These observations lead us to suggest that the OHCs operate more like the envelope detectors in a classical gain-control scheme than like high-frequency sound amplifiers. These findings call for a fundamental reconsideration of the role of the OHCs in cochlear function and the causes of cochlear hearing loss.

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Keywords cochlear amplifier, cochlear mechanics, electromotility, hearing, Mongolian gerbil, neuroscience, outer hair cells, physics of living systems
Persistent URL dx.doi.org/10.7554/eLife.47667, hdl.handle.net/1765/119903
Journal eLife
Vavakou, A. (Anna), Cooper, N.P. (Nigel P.), & van der Heijden, M. (2019). The frequency limit of outer hair cell motility measured in vivo. eLife, 8. doi:10.7554/eLife.47667