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Nonlinearity and amplification in cochlear responses to single and multi-tone stimuli
Elika Fallah1, C Elliott Strimbu2, Elizabeth S Olson3
1Department of Biomedical Engineering Columbia University, New York City, NY, United States.
Hearing Research
|April 25, 2019
Summary
Outer hair cell (OHC) electromotility causes nonlinear mechanical responses in the cochlea. OHC forces amplify sound in the best frequency (BF) region but not below it, explaining cochlear tuning and amplification.
Area of Science:
- Auditory Neuroscience
- Bioacoustics
- Mechanobiology
Background:
- Basilar membrane (BM) mechanical displacements and outer hair cell (OHC) electrophysiology are crucial for cochlear frequency tuning and amplification.
- Understanding the nonlinear behavior of these components is key to deciphering cochlear function.
Purpose of the Study:
- To measure extracellular voltage (VOHC) and displacements within the organ of Corti complex (OCC) in response to single-tone and multi-tone stimuli.
- To investigate the nonlinear mechanical and electrical responses in different cochlear frequency regions (BF and sub-BF).
Main Methods:
- Utilized optical coherence tomography (OCT) to simultaneously measure displacements of various OCC layers in the gerbil cochlea base.
- Applied single-tone and multi-tone auditory stimuli to assess nonlinear responses.
Main Results:
- In the sub-best frequency (sub-BF) region, basilar membrane (BM) motion was linear, while OHC region motion (XOHC) and voltage (VOHC) showed mild to strong nonlinearity, especially with multi-tones.
- In the best frequency (BF) region, BM motion (XBM), VOHC, and XOHC all exhibited classic BF peak nonlinearity.
- Sub-BF nonlinearity was characterized by OHC electromotility saturation, while BF nonlinearity involved OHC forces amplifying the traveling wave.
Conclusions:
- A framework for cochlear nonlinearity is proposed: BF-region nonlinearity amplifies the traveling wave via OHC forces, enhancing propagation.
- Sub-BF nonlinearity is non-amplifying, stemming from OHC electromotility saturation without power transfer to the traveling wave.
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