Phase opposition between inner and outer hair cells and auditory sound analysis

Recordings of single-unit responses in the auditory nerve of normal and kanamycin-treated Mongolian gerbils indicate that inner and outer hair cells of the cochlea interact in phase opposition. After kanamycin treatment, the firing rate in some fibers is increased during the basilar membrane motion toward scala vestibuli, in others, during its motion towards scala tympani. Because of statistical correlation with anatomical changes and characteristic time patterns, the first response polarity is associated with inner hair cells, the second, with outer hair cells. It is shown that normal responses can be reconstructed from the two kinds of responses seen after kanamycin treatment. The phase opposition between inner and outer hair cells, in connection with the expected effect of spiral fibers, provides an explanation for neural sharpening of mechanical filter action in the cochlea.