Contralateral Sound Stimulation Suppresses the Compound Action Potential from the Auditory Nerve in Humans

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Abstract
Background In the past decade, contralateral sound suppression of otoacoustic emissions has been extensively used to study the role of the medial olivocochlear efferent in humans. In most studies, the suppressive effect of contralateral sound stimulation was not greater than 2 to 4 dB. However, the relation between the degree of otoacoustic emission reduction and the neural auditory threshold is unknown. Methods The current study investigates the effect of contralateral sound stimulation by measuring compound action potential response from the auditory nerve during retrosigmoid surgery in humans. Results Although only a small number of subjects responded to contralateral sound stimulation, we report that efferent activation by contralateral sound stimulation results in 10 dB effective neural attenuation. Conclusions Together with previous otoacoustic emission measurements in humans, this result demonstrates that the suppressive effect of contralateral noise suppression is greater when measured with compound action potential than otoacoustic emissions, and that contralateral sound suppressive effect is at least as strong in humans as in animals.