  In the ear, hair cells transform mechanical stimuli into neuronal signals
with great sensitivity relying on certain active processes. Individual hair
cell bundles of non-mammals such as frogs and turtles are known to show
spontaneous oscillation. However hair bundles in vivo must be quiet in the
absence of stimuli, otherwise, the signal is drowned in intrinsic noise. Thus,
a certain mechanism is needed to exist in order to suppress intrinsic noise.
Here, through a model study of elastically coupled hair bundles of bullfrog
sacculi, we show that a low stimulus threshold and a high signal-to-noise ratio
(SNR) can be achieved through the amplitude death phenomenon (the cessation of
spontaneous oscillations by coupling). This phenomenon occurs only when the
coupled hair bundles have inhomogeneous distribution, which is likely to be the
case in biological systems. We show that the SNR has non-monotonic dependence
on the mass of the overlying membrane, and find out that the SNR has maximum
value in the region of the amplitude death. The low threshold of stimulus
through amplitude death may account for the experimentally observed high
sensitivity of frog sacculi in detecting vibration. The hair bundles' amplitude
death mechanism provides a smart engineering design for low-noise
amplification.
