Research on basilar membrane vibration of guinea pigs elicited by direct current pulse

To investigate the electromotility of basilar membrane (BM) of guinea pigs in vivo, a couple of Platinum-iridium wire electrodes were placed into holes drilled in the scala vestibuli and scala tympani on the basal turn of cochlea separately. The organ of Corti was stimulated with rectangular direct current pulses. The displacement and velocity of BM were measured with Laser Doppler velocimeter. The results indicated that the displacement of BM elicited by current moved toward the scala where positive current was injected. The waveform of BM displacement was corresponding to the rectangular pulse of electric current step. Ringing responses could be seen at the onset and offset of current pulse that was the transient responses of outer hair cells. The frequency of the ringing was the same as that of characteristic frequency of partition in BM. It is supposed that the ringing of BM is an active process of depletive energy and participate with cochlear amplifier. In the insensitive cochlea or dead animal, direct current can still elicit a BM displacement but the ringing response is decreased or disappeared. This phenomenon is probably because of metabolic disturbance in damaged outer hair cells. The BM vibration induced by direct current is similar to that of induced by acoustic stimulation, which can transfer to other partition of BM by traveling wave. This characteristic has laid a foundation of electromotile hearing and electrically evoked otoacoustic emission.