Laser interferometric measurements of basilar membrane vibrations in cats using a round window approach

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Abstract
In a round window approach to the basilar membrane, cochleas were opened without bleeding by use of a specially designed microcautery. The state of the cochlea was monitored using C. M. and N1 response. Microscopic gold mirrors were dropped onto the basilar membrane at selected locations without touching the membrane or removing the perilymph. Vibrations of the gold crystals on the basilar membrane were measured with an improved laser interferometer at sound‐pressure levels as low as 30 dB SPL at the tympanic membrane. The observed tuning curves had high‐frequency slopes up to 720 dB/oct and low frequency slopes up to 70 dB/oct. In the past, the sharpness of basilar membrane tuning curves has increased as we progressively reduced the damage to the cochlea. One of the remaining sources of damage in our experiments was the laser beam itself. The intensity of the beam has been reduced by a factor of 100 by redesign of the interferometer. Basilar membrane responses measured with reduced laser damage will be shown. [Supported by N.I.H.]

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