Mechanical nonlinearity in the apical turn of the guinea pig organ of Corti.

Confocal microscopy was used to view the sealed apical turn of the cochlea in a living guinea pig, and to identify the cochlear structures through the intact Reissner's membrane. X, Y and Z coordinates for each point of interest were recorded. A confocal laser heterodyne interferometer measured the cellular vibration in response to acoustical signals applied to the ear. Velocity time waveforms were recorded at 32 frequencies between 25 and 2500 Hz at each point of measurement. To characterize the vibration pattern of the organ of Corti, vibrations at multiple locations along a radial track of the reticular lamina were measured before and after sacrificing the animal. Amplitude and phase tuning curves of the fundamental and the second harmonic, velocity time waveforms, and FFTs of time waveforms are compared before and after sacrifice. The results show that a sharply tuned nonlinear part of the response disappears shortly after sacrifice.