Auditory sensitivity provided by self-tuned critical oscillations of hair cells

We introduce the concept of serf-tuned criticality as a general mechanism f or signal detection in sensory systems. In the case of hearing, we argue th at active amplification of faint sounds is provided by a dynamical system t hat is maintained at the threshold of an oscillatory instability. This conc ept can account for the exquisite sensitivity of the auditory system and it s wide dynamic range as well as its capacity to respond selectively to diff erent frequencies. A specific: model of sound detection by the hair cells o f the inner ear is discussed. We show that a collection of motor proteins w ithin a hair bundle can generate oscillations at a frequency that depends o n the elastic properties of the bundle. Simple variation of bundle geometry gives rise to hair cells with characteristic: frequencies that span the ra nge of audibility. Tension-gated transduction channels, which primarily ser ve to detect the motion of a hair bundle, also tune each cell by admitting ions that regulate the motor protein activity. By controlling the bundle's propensity to oscillate, this feedback automatically maintains the system i n the operating regime where it is most sensitive to sinusoidal stimuli. Th e model explains how hair cells can detect sounds that carry less energy th an the background noise.