Analyzing Cochlear High-frequency Amplification Through a Two-Dimensional Organ of Corti Micro-electro-mechanical Model

The outer hair cell (OHC) in the organ of Corti (OoC) is hypothesized to boost the cochlear responses through electromotility. This hypothesis has been challenged for decades because of the low-pass OHC transmembrane impedance (commonly represented by a resistor-capacitor (RC) circuit). In this study, we analyze an electro-mechanical model of the OoC to explore mechanisms capable of producing high-frequency amplification. By examining the responses, we find that the inertia-like tectorial membrane (TM) shear motion is crucial for the cochlear amplification function. Only when the TM shear motion is inertia-dominant, the amplification gain is critically determined by the structural parameters related to the TM bending motion. The optimal structural parameters may help achieve the high gain seen in the in vivo experiments even with the RC cut-off frequency far below the characteristic frequency. As discussed in recent literature, we also find that the RC filtering of the OHC is a feature of the response rather than some inherent “problem”. The coupling of the OHC electromotility to the TM motion may be crucial for the high- frequency amplification.