Displacement gradients in the lateral region of the organ of Corti dissipate power in the cochlea.

Measurements and models of cochlear mechanics are built upon understanding the fluid mechanics within the cochlear scalae and the fluid interactions within the organ of Corti, basilar membrane (BM), and tectorial membrane, which together make up the organ of Corti complex (OCC). Even in the absence of an active mechanism, the passive cochlea exhibits a traveling wave, which peaks at a location slightly basal of the active peak for a given stimulus frequency, and terminates at a location similar to that of the active traveling wave. The mechanics that result in the termination of the traveling wave are not fully understood. Here, we examine motion in the lateral region of the guinea pig OCC, including the BM, Boettcher's cells (BCs), and Hensen's cells, using optical coherence tomography. We explore this motion as a potential source of viscous forces due to motion gradients. The BCs lie on the BM and were found to move at the same amplitude as the BM. Beyond the BCs, displacement amplitudes exponentially decreased, suggesting that the lateral region motion is "fluid-like." The displacement amplitude decay rates in the lateral region were similar to motion decay rates previously observed in the scala tympani fluid. We compare our results to predictions from a 3D cochlear model and estimate power dissipation as a result of the viscous forces associated with the displacement gradients in the lateral region. The fluid-like motion and viscous forces in the lateral region may serve as a source of power dissipation and thus traveling wave damping.