Fig. 1.

Sound causes contractile motion within the organ of Corti on both a tonic and a cycle-by-cycle basis. (A) Cross-sectional OCT image of the apical cochlear turn. The three scalae (SV, SM, and ST) are indicated, along with Reissner’s membrane (RM), the TM, and the BM. The cellular organ of Corti is situated between the BM and TM. (Scale bar = 50 μm.) (B) The same OCT image with the inferred location of various structures outlined. Displacements parallel to the beam path were measured at locations along the yellow line. (Scale bar = 50 μm.) (C) Schematic of the anatomy. (D and E) Waveforms and spectra of a 9-kHz, 60-dB SPL stimulus and the resulting displacements of locations indicated by black circles in B. Low-pass filtered waveforms (gray lines) reveal the tonic displacements. Waveforms were obtained for 7-ms tones while spectra were obtained using ∼100-ms tones for improved frequency resolution (arrows indicate 0-dB SPL or 0.01 nm, for scale). Responses at the stimulus frequency (f) and its harmonics (2f, 3f, etc.) are labeled, including a 54-kHz component (6f) that was aliased to 46 kHz. (F–I) Cycle-by-cycle displacement magnitudes (F) and phases (G and H), as well as tonic displacements (I), in ∼7-μm steps along the analysis path for a mouse with relatively large harmonics (stimulus = 9-kHz, 60-dB SPL). All phases were referenced to the BM phase at f. Dashed portions of the magnitude and phase curves indicate data falling below the noise floor.