ACOUSTICALLY INDUCED VIBRATIONS OF THE REISSNERS MEMBRANE IN THE GUINEA-PIG INNER-EAR

in the inner ear. the Reissner's membrane separates the scala vestibul i from the scala media and is thus of importance for maintaining a pos itive endocochlear potential. The motion of the membrane is thought to be driven by the Vibrations of the underlying hearing organ caused by a hydromechanical coupling between the structures. Since the Reissner 's membrane is relatively easily accessible in the cochlea its vibrato ry response has been used as a measure of the micromechanical behaviou r of the hearing organ. To determine whether this indirect measure rev ealed the true characteristics of the hearing organ. experiments were performed using laser heterodyne interferometry in an in vitro prepara tion of the guinea-pig temporal bone. Interferometric measurements al the Reissner's membrane and at the surface of the hearing organ direct ly beneath made it possible to compare the mechanical tuning character istics of both structures. It was found that the mechanical response c haracteristics of the Reissner's membrane differed considerably from t he hearing organ. The tuning frequency was different and only minor ch anges in the maximal Vibration amplitude were seen when measuring at d ifferent radial locations. However, the shape of the response curve ch anged with location. The Reissner's membrane response appeared to be a ffected by the mechanical vibrations originating both at the middle ea r ossicles and at the hearing organ. It is concluded that the Reissner 's membrane response is a poor indicator of cochlear mechanics and tha t investigations of cochlear micromechanics should be performed direct ly at the level of the hearing organ.