The mammalian inner ear is exceptional in that it can process sound with high sensitivity and fine frequency resolution over a wide frequency range. The underlying mechanism for this remarkable ability is the "cochlear amplifier," which operates by modifying cochlear micromechanics. Although the exact mechanisms underlying mechanical modifications are unclear, it has been shown that the tectorial membrane plays an important role. In particular, it has been proposed that the tectorial membrane provides a second resonant system in the cochlea. Experiments are proposed to explore whether the tectorial membrane is, in fact, a resonant system and to examine its role in the cochlear-amplifier. To address this problem in an innovative way, an in vitro preparation will be used, the hemicochlea, which allows study of the tectorial membrane in situ. The specific aims of this study are (1) to determine the driving point stiffness of the tectorial at several locations along the cochlea in the hemicochlea, (2) to measure the bulk stiffness of the tectorial membrane in vitro, (3) to confirm the hemicochlea measurements by in vivo experiments at two locations in the basal and the middle turn, and (4) to determine the bending stiffness of the outer hair cell stereocilia bundles. The impedance and stiffness data will allow us to better describe the role of the tectorial membrane in the cochlear-amplifier feedback loop. These experimental results will contribute to our understanding how outer-hair-cell motility and the highly nonlinear cochlear amplifier are controlled, and ultimately, how sound is processed and encoded by the inner ear. This research has broad impact because students and high school teachers will be able to participate by making stiffness measurements of the tectorial membrane in the hemicochlea and in living animals, by interpreting the mechanical impedance measurements of the tectorial membrane and in the field of micromechanics the information may prove useful in developing micromechanical transducers of sound and motion.
