critical self-tuning and efferent control of inner ear hair cells

Hair cells employ active mechanisms to improve their sensitivity to force stimuli. A plethora of measurements indicate that these mechanisms position hair bundles, the mechanosensory organelles of hair cells, near a Hopf bifurcation. The recent disovery that the self-oscillations that embody these mechanisms are suppressed by powerful stimuli corroborates a normal form model for hair bundle dynamics in which a self-tuning process robustly maintains the control parameter in the proximity of the critical point.

Synaptic input to hair cells inhibits self-oscillations but negates the stimulus-induced suppression effect; inspired by the observation of this subtle latter phenomenon, we show that synaptic input can be understood as a distinct process governing the control parameter, and we explore the effects of synaptic input and critical self-tuning on the response of hair bundles to forcing.