Simultaneous Measurements of Pressure and Voltage at the Basilar Membrane Inform Theories of Amplification

A feature of cochlear mechanics is local amplification, in which the response at a given frequency is amplified over a relatively narrow longitudinal extent of the cochlea. The basis for the place-frequency tuning of the amplifier has been explored in cochlear theories, and many models predict realistic level-dependent tuning in BM motion. Modern observations of in vivo active cochlear mechanics also include measurements of local driving pressure, and local extra-cellular voltage. These quantities have been predicted by theories of active cochlear mechanics, and thus the data provide useful modeling constraints. In particular, experimental observations argue against an amplifier that results in highly tuned and nonlinear relationships between pressure:velocity:voltage. These observations are consistent with predictions of some but not all cochlear models. Thus, simultaneous measurements of several cochlear quantities can be very useful in guiding concepts of how cochlear tuning and amplification work.