Medial olivo-cochlear system and tinnitus.

A possible role of the efferent system in the mechanisms of tinnitus generation has been put forward by several authors. A simple method for studying the functioning of this system is to compare the amplitudes of otoemissions with and without mild contralateral stimulation. In a recent communication, Veuillet et al. (1991) reported that, on the side of tinnitus, the efferent system of patients suffering from unilateral tinnitus seems to be less efficient than on the other side. The results presented here correspond to those obtained in the very first tinnitus patients submitted to a research protocol exploring systematically the efferent system. When possible, the effectiveness was tested in two ways: globally, using evoked otoacoustic emissions (EOAEs) and, very precisely in the frequency zone of the tinnitus, using cubic distortion product 2f1-f2. Preliminary results obtained in bilateral and unilateral tinnitus sufferers show that a majority of them exhibits, at least in the proximity of the tinnitus, a lack of effectiveness of the efferent system. In some of them, instead of the suppressive effect, an increasing one was even observed.