Otoacoustic emissions evoked by electrical stimulation

Abstract

Otoacoustic emissions evoked by electrical stimulation of the cochlea were measured in guinea pigs. Alternating current with acoustic frequencies was delivered directly to the scala tympani and the vestibuli of the basal turn by using a constant current stimulator made in our laboratory. The amplitude of the electrically evoked otoacoustic emmisson (EEOAE), which was 21.0 dB SPL in response to 2 kHz electrical stimuli of 120 microArms, was decreased gradually with anoxia of the animal and was reduced to below the noise level by extirpation of the ossiculum. The EEOAEs rose with a delay of 100 microseconds from the beginning of the stimulus, and reached maximum amplitude within three cycles. The output of EEOAE was magnified in a linear manner as the stimulus current increased from 10 to 200 microArms. The averages and standard deviations of the EEOAE output at the stimulus level of 170 microArms in six animals were 20.5 +/- 4.1 dB SPL for 1 kHz, 23.3 +/- 4.8 dB SPL for 2 kHz, 10.5 +/- 6.0 dB SPL for 3 kHz, 17.1 +/- 4.7 dB SPL for 4 kHz, 13.6 +/- 4.4 dB for 5 kHz and 18.3 +/- 4.8 dB SPL for 6 kHz. Measurement of EEOAE, in which stable responses could be obtained with simple and easy preparation, was considered a potential procedure for assessing the electromotility of the cochlear outer hair cells in vivo.