BME Seminar Series: Jong-Hoon Nam, Ph.D.
Micro-Structures of the Organ of Corti Can Create Traveling Waves Along the Cochlear Coil
Professor Jong-Hoon Nam, Ph.D.
The cochlea encodes the frequency and intensity of sounds. It has a remarkable operating range both in frequency and pressure (20 to 20,000 Hz and 20 μPa to 20 Pa). How the cochlea achieve the performance with its limited physical properties has been a long-standing question to scientists. The observation of traveling waves in the cochlea by von Békésy in 1920s underlay the theoretical foundation for cochlear tonotopy (frequency-location relation). In 2000, prestin, a transmembrane protein that is relevant to cochlear amplification, was identified. In this talk, our recent effort to connect these two historical findings (traveling waves and prestin) is introduced.
We have developed a computer model of the organ of Corti, cochlear sensori-epithelium. The model aims to simulate the interaction between the mechano-transducer channels, outer hair cell motility due to prestin motors, and the supporting structures of the organ of Corti. Using the computational model, we observed a new type of propagating waves, an elastic propagating wave, that is independent of the fluid-structure interaction of existing cochlear traveling wave theories. The characteristics of this novel propagating wave, such as the wavelength, speed and phase lag, are remarkably similar to those of observed in the living cochlea. We identified three conditions are required for the existence of our observed elastic propagating wave: 1) the stiffness gradient of the cochlear partition, 2) the elastic longitudinal coupling and 3) the Y-shaped structure in the organ of Corti formed by the outer hair cell, the Deiters cell and the Deiters cell phalangeal process. The results suggest that the micro-mechanical push-pull action of outer hair cells, facilitated by the Deiters cell phalangeal process, can control the tuning and amplification by modulating the cochlear traveling wave.