An alternative pathway for delivery of power by outer hair cells to cochlear traveling waves

In vivo measurements show that the basilar membrane (BM) exhibits sharp frequency tuning and high sensitivity to low-level stimuli. This has led most cochlear theories to assume that outer hair cells (OHCs) amplify traveling waves by delivering power directly to the BM. However, recent experiments revealed that the main bodies of Deiters cells (DCs), which are sandwiched between the OHCs and the BM, deform significantly in response to acoustic inputs. These findings challenge the hypothesis that power is transmitted by OHCs to the BM through the DCs. In this work, we consider a cochlear model that includes a micromechanical model of the organ of Corti with deformable DCs. The micromechanical model includes not only the BM, OHCs and DCs, but also other components of the organ of Corti, including the reticular lamina (RL) and pillar cells (PCs). We find that the amplitude and phase of the OHC-DC junction is consistent with in vivo measurements only if (1) the DC stiffness is comparable to that of OHCs; and (2) the joint between the RL and PCs is relatively stiff. Under these conditions, the model predicts that OHC electromotility does not deliver power to the BM through the classical OHC-DC-BM pathway, but rather through an alternative pathway through the RL and PCs. This result points to a new theoretical framework in which the RL and PCs, rather than DCs, serve as the primary conduit for the transfer of OHC-generated power to the BM and offers new insight into how the cochlea may achieve its remarkable sensitivity and frequency selectivity.