Outer hair cell somatic, not hair bundle, motility is the basis of the cochlear amplifier

Sensitivity, dynamic range and frequency tuning of the cochlea are attributed to amplification involving outer hair cell stereocilia and/or somatic motility. We measured acoustically and electrically elicited basilar membrane displacements from the cochleae of wild-type and TectaENT/ENT mice, in which stereocilia are unable to contribute to amplification near threshold. Electrically elicited responses from TectaENT/ENT mice were markedly similar to acoustically and electrically elicited responses from wild-type mice. We conclude that somatic, and not stereocilia, motility is the basis of cochlear amplification.