Hydromechanical Structure of the Cochlea Supports the Backward Traveling Wave in the Cochlea In Vivo.

Fangyi Chen,Xiaojie Yang,Allyn Hubbard,Alfred Nuttall,Dingjun Zha

doi:10.1155/2018/7502648

Abstract

The discovery that an apparent forward-propagating otoacoustic emission (OAE) induced basilar membrane vibration has created a serious debate in the field of cochlear mechanics. The traditional theory predicts that OAE will propagate to the ear canal via a backward traveling wave on the basilar membrane, while the opponent theory proposed that the OAE will reach the ear canal via a compression wave. Although accepted by most people, the basic phenomenon of the backward traveling wave theory has not been experimentally demonstrated. In this study, for the first time, we showed the backward traveling wave by measuring the phase spectra of the basilar membrane vibration at multiple longitudinal locations of the basal turn of the cochlea. A local vibration source with a unique and precise location on the cochlear partition was created to avoid the ambiguity of the vibration source in most previous studies. We also measured the vibration pattern at different places of a mechanical cochlear model. A slow backward traveling wave pattern was demonstrated by the time-domain sequence of the measured data. In addition to the wave propagation study, a transmission line mathematical model was used to interpret why no tonotopicity was observed in the backward traveling wave.

Highlights

Ears hear sound and generate sound, which is called the otoacoustic emission (OAE) and was discovered in 1978 [1]
The backward traveling wave theory, which postulates that OAE-induced waves travel slowly along the basilar membrane (BM), is widely accepted as an explanation of the propagation of the OAE [1, 2]
We found that the phase of the measured BM motion showed a consistent lag with the increase of the distance from the vibration source

Summary

Introduction

Ears hear sound and generate sound, which is called the otoacoustic emission (OAE) and was discovered in 1978 [1]. In the compression wave theory, the slow-speed propagation of the backward transversal wave motion of the BM is replaced by a fast-fluidic compression wave and experimental time/phase differences are accounted for by mechanisms independent of the wave To date, it is still an open question about the OAE path. In relation to the backward propagation of the OAE, von Békésy discovered that the wave on the BM always traveled from the base to the apex, even the stimulus (the stapes vibration) was placed at the apex of the cochlea This so-called paradoxical wave was a hurdle that prevented people from believing that the OAE can propagate along the BM backward at the time

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Conclusion