Vibratory responses to outer hair cell-generated distortion products along the width of the mouse organ of Corti

Abstract

Mammalian hearing sensitivity depends on the amplification of cochlear vibrations by outer hair cells (OHCs). OHCs are thought to generate amplifying forces through electromotility, i.e., voltage-driven changes in cell length, though how exactly these forces influence the motion of the surrounding organ of Corti structures remains incompletely understood. Here, in the mouse cochlear apex, optical coherence tomography was used to characterize electromotility-induced vibrations along the axis of the OHCs and along the widths of both the basilar membrane (BM) and reticular lamina (RL). Two-tone stimuli were used to elicit OHC-driven vibrations at a variety of intermodulation distortion-product (DP) frequencies. For a wide range of DP frequencies, out-of-phase motions were observed between the bottoms and tops of the OHCs, as well as between the tops of the OHCs and the lateral supporting cells. However, along the BM, phase variations were only observed at frequencies above the characteristic frequency (CF), with in-phase motions being observed at lower frequencies. The data indicate that OHCs can rapidly deform the top of the organ of Corti, while the BM response is more complex, likely being dominated by traveling-wave energy at and below the CF. [Work supported by NIH/NIDCD R21 DC019209 and the Hearing Health Foundation.]