Revealing the actions of the human cochlear basilar membrane at low frequency

The basilar membrane (BM) is the key infrastructure that supports the microstructure of cochlear acoustic function, and its interaction with lymph in the cochlea involves a complex, highly nonlinear coupling motion and energy conversion. In 1928, Nobel Laureate Gordon von Békésy experimented and first discovered the traveling wave motion of the BM, thus uncovering the mystery of BM motion. However, with the further development of experimental technology in recent years, scientists have discovered that the traveling wave motion does not explain many experimental observations and phenomena associated with the detection of low-frequency sounds by the cochlea. Because the cochlea is very small and complex, Békésy could only obtain medium- and high-frequency motion data for the BM but not low-frequency motion data. Based on a theory of mathematical physics and biology combined with data from medical and modern light source imaging experiments, a theoretical model of the spiral cochlea and a numerical model that conforms to the real human ear were established. The results reproduce the known traveling wave motion of the BM. Meanwhile, an exciting new finding has revealed a standing wave motion pattern at low frequencies. This newly discovered motion pattern intrinsically explains many experimental observations that could not be explained by the traveling wave theory. These results not only complement the low-frequency motion characteristics of the BM, but also probably reveal the mechanism of active phonoreceptive amplification in the cochlea, which has been a difficult problem to unravel in otology medicine. •By the tensor mapping, a 3-D spiral cochlea geometric model was established for analytical analysis.•The eikonal equation and transport equation of the wave motion of the BM were obtained.•By our self-program, the lymph pressure and amplitude and phase of the BM were obtained.•The geometric shapes and materials in accord with the numerical model of real human ear are established.•Newly standing wave mode of BM in cochlea at LF is found, which is unknown difficulty concerned up to now.