SOUND-INDUCED DISPLACEMENT RESPONSES IN THE PLANE OF THE ORGAN OF CORTI IN THE ISOLATED GUINEA-PIG COCHLEA

Sound-induced displacement responses in the plane of the organ of Cort i were studied in the apical turn in the isolated temporal-bone prepar ation of the guinea-pig cochlea. Swept sinusoidal sound stimuli (100-5 00 Hz) were delivered closed-field to the external auditory meatus. Th e surface of the organ of Corti was continuously monitored using a CCD video camera. Displacement responses in the plane of the organ of Cor ti were determined by analyzing the change of the location of the cell s (pixel-by-pixel) within the visual field of the microscope. Displace ment responses followed the stimulus amplitude and were observable at Hensen's cells, three rows of outer hair cells and inner hair cells. T he most prominent displacement responses were over the outer hair cell s; the maximum amplitude was 0.6-1.7 mu m at 100 dB SPL. Tuned displac ement responses were found; the Q(10 dB) was 1.3 +/- 0.6. The best fre quency was tonotopically organized, decreasing toward the apex with a space constant of 0.4-0.9 mm/oct. The motion was directed either stria l-apically or strial-basally in a frequency dependent manner. With the aid of laser interferometric measurements of the transverse displacem ent, it was concluded that sound stimulation does not induce slow DC m otion in the organ of Corti for the isolated temporal-bone preparation .