The cochlea is selective to individual frequencies of sound pressure, as sensitive as physical limits allow, and instantaneously adaptive to a wide range of stimulation levels. The basis for cochlear operation must lie in the mechanical and electromechanical properties of the cochlear partition, but is poorly understood. The proposed work seeks to characterize mechanical properties of the partition, especially as they relate to the frequency tuning and sensitivity of cochlear motion. The experimental animal will of the Mongolian gerbil, whose anatomy allows a 0.5mm longitudinal extent of the cochlear partition to be accessed through the round window opening. Two sets of measurements will be performed, both directed at determining the partition's mechanical impedance, which is defined as the ratio of pressure or force across the partition to the motion of the partition. In the first set of measurements, the impedance will be directly measured at a point as the force required to locally vibrate the partition. Point impedance will be measured at nine radial positions spanning the partition, and at two to three longitudinal positions over 0.5 mm. Vibration frequencies will vary from 100 to 1000 Hz. The radial variation in impedance will be directly related to the partition anatomy, indicating which partition elements contribute substantially to the impedance. The longitudinal variation in impedance will be analyzed with respect to the predicted variation, based on longitudinal variations in partition width and characteristic frequency. The second set of measurements map intracochlear pressure in scala tympani in three dimensions. Scala tympani pressure will be measured through the round window opening, close to the cochlear partition, at frequencies through the characteristic frequency (30 - 40 kHz in this region). Scala tympani pressure will be referenced to pressure at one point in scala vestibuli, relatively remote from the partition. The spatial, level, and frequency dependent variations in pressure will inform cochlear models by constraining the form of the partition impedance, and addressing the issue of active-vs-passive cochlear operation. The concerted analysis of the two sets of measurements will suggest modes of partition motion, and the micromechanical basis for that motion. The cochlea is a unique organ, but its nonlinear, dynamic operation reflects general principles and strategies for signal retrieval, sorting and transduction. The goal of these measurements is to understand the complex workings of the cochlea, which, beyond its intrinsic value, is of fundamental value to the understanding of physiological systems, with extension to the design of prosthetics and sensing systems in general.

Agency
National Institute of Health (NIH)
Institute
National Institute on Deafness and Other Communication Disorders (NIDCD)
Type
First Independent Research Support & Transition (FIRST) Awards (R29)
Project #
5R29DC003130-02
Application #
2377588
Study Section
Hearing Research Study Section (HAR)
Project Start
1996-03-01
Project End
2001-02-28
Budget Start
1997-03-01
Budget End
1997-08-31
Support Year
2
Fiscal Year
1997
Total Cost
Indirect Cost
Name
Princeton University
Department
Physics
Type
Schools of Arts and Sciences
DUNS #
002484665
City
Princeton
State
NJ
Country
United States
Zip Code
08544
Decraemer, W F; de La Rochefoucauld, O; Funnell, W R J et al. (2014) Three-dimensional vibration of the malleus and incus in the living gerbil. J Assoc Res Otolaryngol 15:483-510
Shera, Christopher A; Olson, Elizabeth S; Guinan Jr, John J (2011) On cochlear impedances and the miscomputation of power gain. J Assoc Res Otolaryngol 12:671-6
de La Rochefoucauld, Ombeline; Olson, Elizabeth S (2010) A sum of simple and complex motions on the eardrum and manubrium in gerbil. Hear Res 263:9-15
de La Rochefoucauld, Ombeline; Kachroo, Puja; Olson, Elizabeth S (2010) Ossicular motion related to middle ear transmission delay in gerbil. Hear Res 270:158-72