Waves on Reissner's membrane can convey otoacoustic emissions
Sound is detected and converted into electrical signals within the ear. The cochlea not only acts as a passive detector of sound, however, but can also produce tones itself. These otoacoustic emissions are a striking manifestation of the cochlea’s mechanical active process. A controversy remains concerning how these mechanical signals propagate back to the middle ear, from which they are emitted as sound. We combined theoretical and experimental studies to show that mechanical signals can be transmitted by waves on Reissner's membrane, an elastic structure within the cochea. We developed a theory for wave propagation on Reissner's membrane and its role in otoacoustic emissions. Employing a scanning laser interferometer, we measured traveling waves on Reissner's membrane in the gerbil, guinea pig, and chinchilla. The results accord with the theory and thus support a role for Reissner's membrane in otoacoustic emissions.
During stimulation with sound (left), traveling waves propagate on the hydrodynamically coupled basilar membrane and Reissner's membrane. When distortion products arise during two-tone stimulation (right), Reissner's membrane can bear short-wavelength traveling waves that transmit otoacoustic emissions.