Evidence for corticofugal modulation of peripheral auditory activity in humans.

Active cochlear micromechanisms, involved in auditory sensitivity, are modulated by the medial olivocochlear efferent system, which projects directly onto the organ of Corti. Both processes can be assessed non-invasively by means of evoked otoacoustic emissions. Animal experiments have revealed top-down control from the auditory cortex to peripheral auditory receptor, supported by anatomical descriptions of descending auditory pathways from auditory areas to the medial olivocochlear efferent system and organ of Corti. Through recording of evoked otoacoustic emissions during presurgical functional brain mapping for refractory epilepsy, we showed that corticofugal modulation of peripheral auditory activity also exists in humans. In 10 epileptic patients, electrical stimulation of the contralateral auditory cortex led to a significant decrease in evoked otoacoustic emission amplitude, whereas no change occurred under stimulation of non-auditory contralateral areas. These findings provide evidence of a cortico-olivocochlear pathway, originating in the auditory cortex and modulating contralateral active cochlear micromechanisms via the medial olivocochlear efferent system, in humans.