Nonlinear vibrations in the apex of guinea-pig cochlea

The apical turn of a living guinea-pig cochlea was opened gently and ¯uid coupled to the objective lens of a confocal microscope-interferometer. The reticular lamina was viewed through the intact ReissnerÕs membrane. Mechanical vibrations were measured at identi®ed cellular locations, in response to tones applied with an acoustic transducer coupled to the ear canal. Time waveforms were measured at an outer and middle HensenÕs cell over a wide intensity and frequency range. The time waveforms were distorted and the magnitude and number of harmonics in the FFTs of waveforms were high, indicating a strong nonlinearity. However, the amplitude of the fundamental component of the response increased nearly linearly with sound pressure. This paper examines the origin and the role of the nonlinear components in the cochlear function