# Experimental Theoretical Studies of Cochlear Mechanisms

> **NIH NIH R01** · MASSACHUSETTS INSTITUTE OF TECHNOLOGY · 2024 · $369,133

## Abstract

Project Summary
Based on its strategic location, the tectorial membrane (TM) has long been thought to play an essential role in
hearing, but the important cochlear mechanisms remain unclear. We propose research to improve our understanding
of the functional role of the TM in determining (1) the remarkable properties of normal hearing — including its
exquisite sensitivity and frequency selectivity — as well as (2) the hearing loss associated with genetic mutations
of the TM and other cochlear pathologies. Conventional models of cochlear mechanics represent the TM as a
viscoelastic solid, and while the importance of both viscosity and elasticity is well established, these models do not
account for the central role of water in this tissue. The TM is a gel: 97% water contained in a macromolecular matrix
of proteins and sugar groups. Recent studies show that sound-induced motions of water through this macromolecular
matrix plays a critical functional role in determining the timing of mechanical responses – and this timing is central
to determining the frequency selectivity that is a hallmark of mammalian hearing.
The proposed research will measure and characterize the important consequences of the gelatinous nature of the
TM, i.e., its poroelastic properties. This work is organized in two related aims. The first investigates mechanical
consequences of poroelasticity. We have developed a technique based on atomic force microscopy to measure
mechanical properties of the TM at the level of single hair bundles. We will apply this technique to characterize
poroelasticity in TMs from normal-hearing rodents, as well as mice with genetic disorders of hearing. Our second
aim focuses on the role of ions (especially calcium) that are dissolved in the liquid phase of the TM. The TM has
been shown to concentrate calcium at levels well in excess of those in the surrounding endolymph. Changes in ionic
concentrations have been shown to alter the electro-mechanical properties of the TM, and will thereby also affect
the closely apposed hair bundles of hair cells. The local concentration of calcium is known to affect not only
the sound-induced receptor potentials of hair cells, but also adaptation processes that are necessary to maintain the
remarkable sensitivity of hearing.
Results from these studies will increase our understanding of the cochlear mechanisms that underlie both normal and
impaired hearing. This knowledge has important practical applications for the delineation of inner-ear disorders (and
concomitant suggestions for treatment) and for the design of speech-processing devices such as cochlear implants,
hearing aids, and speech-recognition systems.

## Key facts

- **NIH application ID:** 10731388
- **Project number:** 5R01DC000238-38
- **Recipient organization:** MASSACHUSETTS INSTITUTE OF TECHNOLOGY
- **Principal Investigator:** Dennis M Freeman
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $369,133
- **Award type:** 5
- **Project period:** 1984-06-01 → 2027-11-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10731388

## Citation

> US National Institutes of Health, RePORTER application 10731388, Experimental Theoretical Studies of Cochlear Mechanisms (5R01DC000238-38). Retrieved via AI Analytics 2026-05-27 from https://api.ai-analytics.org/grant/nih/10731388. Licensed CC0.

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