Velocity and displacement coupling of mammalian inner hair cells and the mechanical resonance of the free-standing stereocilia.

Some controversy still exists as to whether the inner hair cells of the mammalian cochlea respond to the velocity or displacement of the basilar membrane or to a combination of these over their operating frequency range. A comparison between the nonlinear properties of the receptor potentials within inner hair cells of the basal turn of the guinea pig cochlea and the potentials recorded within the scala media of the same animals for stimulus frequencies between 200 and 3,200 Hz provides evidence that these inner hair cells change from velocity sensitivity to displacement sensitivity at about 1,000 Hz. We infer from this that viscosity within the subtectorial space is high enough to preclude mechanical resonance of the freestanding stereocilia of these cells as a frequency-selective mechanism within the mammalian cochlea.