Longitudinal Vibrations in the Organ of Corti are Limited to Its Core.

Abstract

Purpose: The goal of this research was to determine where in the organ of Corti (ooC) sound-induced, longitudinal vibrations occur, and how they depend on the health of the cochlea.

Methods: Sound-evoked vibrations of the ooC in the cochlea's middle turn of adult anesthetized gerbils were measured using optical coherence tomography (OCT). Vibratory responses, evoked with acoustic tone complexes, were recorded at multiple, closely spaced (20 μm), tonotopic locations which changed the "viewing angle" of the vertical OCT beam re. the longitudinal motion. After spatial alignment of the responses, within-ooC regions exhibiting sound-induced longitudinal motion were identified from a conspicuous 180° phase flip.

Results: Longitudinal motion was restricted to the outer hair cells (OHC), Deiters' cells and the tunnel of Corti (i.e., the ooC's "core"). They were frequency and level-independent but did depend on the ear's metabolic state; after death, they disappeared.

Conclusion: There can be little doubt about the presence of longitudinal motions within the cochlea. Their disappearance postmortem and spatially restricted occurrence suggest these longitudinal vibrations arise from active processes within the OHC. Whether this involves cycle-by-cycle feedback or some other, as-of-yet undetermined, mechanism remains to be resolved.