Cochlear wave propagation under acoustical and electrical stimulations

Input sounds to the mammalian ear produce waves that travel from the base to the apex of the cochlea. These traveling waves stimulate the microstructure of the organ of Corti (OoC) in the center of the cochlea. The interplay between the traveling wave and a distinct nonlinear amplification process boosts the cochlear responses and enables sound processing over a broad frequency and intensity ranges. The in vivo electrical and acoustical stimulations have extensively been used to identify the underlying amplification process. In order to interpret the experimental data and propose a precise active mechanism, a comprehensive three-dimensional model of the cochlea is used. Our model predicts that applying an intracochlear excitation (electrical current or mechanical force) on a location along the cochlea generates a dispersive wave propagation in both forward and reverse directions. It is also found that the wave propagation in the cochlea is nonreciprocal when stimulated by an electrical current applied in the OoC. This effect is attributed to the feed-forward mechanism, mediated by a longitudinal electrical cable in our model. [This work was supported by NIH Grant Nos. DC-004084 and T32DC-00011.]