Reticular lamina vibrations in the apical turn of a living guinea pig cochlea.

The reticular lamina of the apical turn of a living guinea pig cochlea was viewed through the intact Reissner's membrane using a slit confocal microscope. Vibrations were measured at selected identified locations with a confocal heterodyne interferometer, in response to tones applied with an acoustic transducer coupled to the ear canal. The position coordinates of each location were recorded. Mechanical tuning curves were measured along a radial track at Hensen's cells, outer hair cells, inner hair cells and at the osseous spiral lamina, over a frequency range of 3 kHz, using five sound pressure levels (100, 90, 80, 70 and 60 dB SPL). The carrier to noise ratio obtained throughout the experiments was high. The response shape at any measuring location was not found to change appreciably with signal level. The response shape also did not change significantly with the radial position on the reticular lamina. However, the response magnitude increased progressively from the inner hair cell to the Hensen's cell. The observed linearity of response at the fundamental frequency is explained by the presence of negative feed back in the apical turn of the cochlea.