[Exploration of the efferent system in man: basic and clinical results]

Since 1989, the exploration of the medial efferent system has been possible in human by using a non-invasive technique consisting in the association of the contralateral acoustic stimulation and the evoked otoacoustic emissions (EOAEs). This exploration presents a great interest for fundamental auditory research because it is the sole means of exploring in human these cochlear efferent neurons synapsing at the base of the outer hair cells. The function of this system is still unknown. The interest of such an exploration in clinical research is now becoming obvious such that it would be not only useful but also necessary to establish a precise diagnosis in particular pathologies. The aim of the present paper is to expose basic results obtained on the medial efferent system in normal subjects and above all to present findings for pathological ears, among which figure in particular: retrocochlear pathologies, hyperacousia, noise-induced hearing loss, tinnitus. In addition to the diagnostic interest of the exploration of the medial efferent system, a knowledge of its functioning will probably allow its role in audition to be determined.