Collective Modes in the Mammalian Cochlea

In mammalian hearing, sound produces surface waves along the basilar membrane, separating the cochlea into two fluid-filled compartments. It is well known that the underlying wave equation supports localized modes that are sharply peaked in position. Recently, we showed by numerical investigation that there is another set of collective “extended modes” (https://arxiv.org/pdf/2407.14496). Localized modes can be tuned almost independently to the edge of instability by local hair cell activity, in contrast to the extended modes, which couple to hair cell activity along the entire cochlea. Here, we present an analytic understanding of this enlarged mode structure and demonstrate how stability constrains possible forms of active feedback.