Changes in the Cochlear Microphonic of the Guinea Pig Produced by Mechanical Factors in the Inner Ear

The cochlear microphonics of the guinea pig have been recorded by means of differential intracochlear electrodes located in various turns of the cochlea. Since it has been shown by Békésy that the cochlear-microphonic voltage is proportional to the displacement of the basilar membrane, it is, thus, possible to study the changes in the mechanical movements of the cochlear partition. Mechanical alterations were produced by increase of the fluid pressure inside the cochlea and by local pressure on the basilar membrane. Increased intracochlear pressure produces a selective decrease in the microphonics recorded from the apical part of the cochlea, and when this decrease becomes very large a phase shift is also observed. Touching the basilar membrane with a guinea-pig hair in the basal turn modifies the potential recorded in the same region, but leaves unchanged the microphonics recorded in the upper parts. Pressing on the basilar membrane in the second turn modifies the microphonics recorded in the apical part, but not the microphonics of the basal turn. Rather large destructions of the apical parts of the cochlea modify only slightly, or not at all, the microphonics from the basal part of the cochlea. These various effects are discussed in the light of the mechanisms and the models described by Békésy.