Cochlear wave dispersion reveals partition micromechanics

Cochlear traveling waves are a fundamental aspect of mammalian hearing, enabling frequency selectivity. However, incorporating micromechanical interactions between the cells, membranes, and fluids that comprise the cochlear partition presents a challenge when accounting for this selectivity and other macro-scale response properties. The traveling wave can be characterized by its dispersion, which is the relationship between its wavenumber and frequency. One objective was to investigate how organ of Corti structural components influence wave dispersion. To achieve this, we adapted a conventional three-dimensional tapered cochlear box model by incrementally adding morphological characteristics that constitute the partition. Initially a flexible plate, the partition transformed to incorporate a tectorial membrane and inner spiral sulcus. Our secondary objective was to predict the dispersion for each variation using a reduced-length model (slice model). We observed that stiffness and the optimal frequency increased across variations, while wave dispersion remained unchanged relative to the optimal frequency. We also discovered that eigenfrequency analysis, using Floquet boundary conditions, accurately predicted the dispersion for each variation and revealed the existence of other propagating waves including a tectorial membrane transverse mode. These results underscore the significance of analyzing cochlear wave propagation from capturing macromechanical response properties thereby facilitating investigations of micromechanical interactions in reduced-length models.