Electromotile outer hair cell (OHC) feedback provides the sensitivity and
sharp frequency tuning of the cochlea. Basilar membrane displacements in response
to characteristic frequency (CF) tones were measured with an interferometer
at up to 15 locations across the basilar membrane width in the basal turn
of the guinea pig cochlea. For CF tones, basilar membrane vibrations were
largest beneath the OHCs; these phase-led vibrations beneath outer pillar
cells and adjacent to the spiral ligament by ~90°. Post mortem,
responses measured beneath the OHCs were reduced by up to 65 dB, and the basilar
membrane moved with similar phase across its entire width. We suggest OHCs
amplify basilar membrane responses to CF tones when the basilar membrane moves
at maximum velocity.
