Spatial profiles of sound-evoked vibration in the gerbil cochlea

Spatial profiles of sound-evoked vibration were investigated in the basal turn and hook region of the gerbil cochlea. Responses to multi-Tone "zwuis" stimuli were recorded through the intact round window membrane using optical coherence tomography. Both radial/transverse and longitudinal variations in the responses (i.e. spatial profiles) were mapped throughout the organ of Corti (OoC) and basilar membrane (BM) complex. Spatial profiles depended on both stimulus frequency and sound pressure level, with different structures within the BM/OoC complex exhibiting subtle differences in tuning. The current paper focusses on the radial variations, which confirm previous reports that the BM responds in a uni-modal fashion [1]: maximum BM displacements were always observed between the feet of the outer pillar cells and the midline of the BM, very near the point where the arcuate and pectinate zones (AZ, PZ) of the BM meet. The radial mode-shape of the BM thus resembles that of an asymmetric pair of saloon doors, with the PZ being roughly twice as wide as the AZ. Responses evaluated from structures slightly deeper into the OoC had radial profiles that were more complex (i.e. multi-modal), occasionally bearing some resemblance to the findings reported by other investigators (who were reportedly studying the BM itself, e.g. [2]). The longitudinal variations in the BM/OoC responses resembled those observed in numerous previous reports (e.g. [3,4]), and form the focus of a companion paper [5].

• View at Publisher
• View at Scopus