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The Nonlinear Dynamics of Coupled Hair Bundles


The sensitivity of the auditory system depends in part on the active response of hair cells in the inner ear. Individual hair bundles display frequency selectivity and compressive nonlinearity in response to stimuli. In many auditory and vestibular end organs, the hair bundles are coupled by overlying structures. This motivates our study on how coupling affects the hair bundle sensitivity. We coupled two to four spontaneously oscillating bundles with a microbead, and applied mechanical stimuli to the group. Under these coupling conditions, innate oscillations synchronized, and oscillations became more regular. Furthermore, the synchronized bundles exhibited broad frequency selectivity, over a bandwidth encompassing each bundle’s natural frequency. The amplitude of the response also showed compressive nonlinearity. On the other hand, similar experiments performed on bundles coupled under the otolithic membrane showed completely linear behavior. Our data suggests that coupling plays a role in the dynamics and sensitivity of a nonlinear system, though the effect depends on the scale of coupling.

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