Tunning to Criticality in the Cochlea with Local Information

The human ear can detect sounds over a vast frequency range with incredible sensitivity. To explain these properties, it has been suggested that individual hair cells operate near an oscillatory instability, a so-called Hopf bifurcation. However, resonating modes are determined primarily by the passive hydrodynamics and mechanical stiffness of the cochlea, with active processes in individual hair cells only serving to counteract dissipative forces. In this picture, every frequency must have a mode tuned close to a Hopf bifurcation, but each hair cell impacts every mode to varying extents. It is an open question how these coupled hair cells could tune their behavior so as to bring the entire cochlea to this line of Hopf bifurcations. To approach this question, we develop a model where hair cells collectively tune their active processes while only using information measurable from their location on the cochlea. Our work suggests a new perspective on the hearing mechanism: Instead of individual hair cells being critical, their concerted individual action tunes the whole cochlea to a critical point revealing a collective organization principle in the inner ear.