Noise in the Outer Hair Cell and Gain Control in the Ear

We present a minimal model of a local resonance inside the mammalian cochlea in which a feedback loop containing an outer hair cell is poised on a dynamical instability. This model results in an amplifier essentially equivalent to a van der Pol oscillator in its weakly nonlinear limit. The feedback loop automatically seeks the instability where gain and gain compression are optimized. The outer hair cell’s average membrane potential is the control parameter which sets amplifier gain. We briefly investigate noise sources inside the outer hair cell which contribute to the feedback loop oscillating in a noise‐driven limit‐cycle. Experimentally this limit‐cycle is increased by 3 to 5 times in high external noise environments. A half millivolt shift due to efferent stimulation can account for the observed 50 percent reduction in both the size of the noisy limit‐cycle oscillation and the feedback loop gain.