BIOPHYSICAL THEORY AND MODELING |
The role of organ of Corti mass in passive cochlear tuning
Ombeline de La Rochefoucauld 1* and Elizabeth S Olson 2
1 Dept. of Otolaryngology, Head and Neck Surgery, Columbia University, New York
2 Dept. of Otolaryngology, Head and Neck Surgery and Biomedical Engineering, Columbia University
* To whom correspondence should be addressed. E-mail: or2107{at}columbia.edu.
Submitted on March 29, 2007
Revised on May 8, 2007
Accepted on 20 July 2007
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Abstract |
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The mechanism for passive cochlear tuning remains unsettled. Early models considered the organ of Corti complex (OCC) as a succession of spring-mass resonators. Later, traveling wave models showed that passive tuning could arise through the interaction of cochlear fluid mass and OCC stiffness without local resonators. However, including enough OCC mass to produce local resonance enhanced the tuning by slowing and thereby growing the traveling wave as it approached its resonant segment. To decide whether the OCC mass plays a role in tuning, the frequency variation of the wavenumber of the cochlear traveling wave was measured (in vivo, passive cochleae) and compared to theoretical predictions. The experimental wavenumber was found by taking the phase difference of basilar membrane motion between two longitudinally-spaced locations and dividing by the distance between them. The theoretical wavenumber was a solution of the dispersion relation of a 3D cochlear model with OCC mass and stiffness the free parameters. The experimental data were only well fit by a model that included OCC mass. However, as the measurement position moved from a best frequency place of 40 to 12 kHz the role of mass was diminished. The notion of local resonance seems to only apply in the very high frequency region of the cochlea.
Key Words:
3D cochlear model, basilar membrane, gerbil, organ of Corti, tuning, wavenumber
