MECHANICAL RESPONSE CHARACTERISTICS OF THE HEARING ORGAN IN THE LOW-FREQUENCY REGIONS OF THE COCHLEA

1. With the use of an in vitro preparation of the guinea pig temporal bone, in which the apical turns of the cochlea are exposed, the mechan ical and electrical responses of the cochlea in the low-frequency regi ons were studied during sound stimulation. 2. The mechanical character istics were investigated in the fourth and third turns of the cochlea with the use of laser heterodyne interferometry, which allows the vibr atory responses of both sensory and supporting cells to be recorded. T he electrical responses, which can be maintained for several hours, we re recorded only in the most apical turn. 3. In the most apical turn, the frequency locations and shapes of the mechanical and electrical re sponses were very similar. 4. The shapes of the tuning curves and the spatial locations of the frequency maxima in the temporal bone prepara tion compared very favorably with published results from in vivo recor dings of hair cell receptor potentials and sound-induced vibrations of the Reissner's membrane. 5. Compressive nonlinearities were present i n both the mechanical and the electrical responses at moderate sound p ressure levels. 6. The mechanical tuning changed along the length of t he cochlea, the center frequencies in the fourth and third turns being similar to 280 and 570 Hz, respectively. 7. The mechanical responses of sensory and supporting cells were almost identical in shape but dif fered significantly in amplitude radially across the reticular lamina.