title: Coupling a sensory hair-cell bundle to cyber clones enhances nonlinear amplification.
abstract: The vertebrate ear benefits from nonlinear mechanical amplification to operate over a vast range of sound intensities. The amplificatory process is thought to emerge from active force production by sensory hair cells. The mechano-sensory hair bundle that protrudes from the apical surface of each hair cell can oscillate spontaneously and function as a frequency-selective, nonlinear amplifier. Intrinsic fluctuations, however, jostle the response of a single hair bundle to weak stimuli and seriously limit amplification. Most hair bundles are mechanically coupled by overlying gelatinous structures. Here, we assayed the effects of mechanical coupling on the hair-bundle amplifier by combining dynamic force clamp of a hair bundle from the bullfrog's saccule with real-time stochastic simulations of hair-bundle mechanics. This setup couples the hair bundle to two virtual hair bundles, called cyber clones, and mimics a situation in which the hair bundle is elastically linked to two neighbors with similar characteristics. We found that coupling increased the coherence of spontaneous hair-bundle oscillations. By effectively reducing noise, the synergic interplay between the hair bundle and its cyber clones also enhanced amplification of sinusoidal stimuli. All observed effects of coupling were in quantitative agreement with simulations. We argue that the auditory amplifier relies on hair-bundle cooperation to overcome intrinsic noise limitations and achieve high sensitivity and sharp frequency selectivity.
authors.affiliation: Laboratoire Physico-Chimie Curie, Centre National de la Recherche Scientifique, Institut Curie, Université Pierre et Marie Curie, 75005 Paris, France.
authors.forename: Jérémie
authors.initials: J
authors.lastname: Barral
authors.forename: Kai
authors.initials: K
authors.lastname: Dierkes
authors.forename: Benjamin
authors.initials: B
authors.lastname: Lindner
authors.forename: Frank
authors.initials: F
authors.lastname: Jülicher
authors.forename: Pascal
authors.initials: P
authors.lastname: Martin
mesh_terms: D006198:Hair Cells, Auditory; D046569:Neuroepithelial Cells / Q000502:physiology*; D009622:Noise
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