Anomalous Brownian motion discloses viscoelasticity in the ear's mechanoelectrical-transduction apparatus.
The ear detects sounds so faint that they produce only atomic-scale displacements in the mechanoelectrical transducer, yet thermal noise causes fluctuations larger by an order of magnitude. Explaining how hearing can operate when the magnitude of the noise greatly exceeds that of the signal requires an understanding both of the transducer's micromechanics and of the associated noise. Using microrheology, we characterize the statistics of this noise; exploiting the fluctuation-dissipation theorem, we determine the associated micromechanics. The statistics reveal unusual Brownian motion in which the mean square displacement increases as a fractional power of time, indicating that the mechanisms governing energy dissipation are related to those of energy storage. This anomalous scaling contradicts the canonical model of mechanoelectrical transduction, but the results can be explained if the micromechanics incorporates viscoelasticity, a salient characteristic of biopolymers. We amend the canonical model and demonstrate several consequences of viscoelasticity for sensory coding.
Howard Hughes Medical Institute and Laboratory of Sensory Neuroscience, The Rockefeller University, 1230 York Avenue, New York, NY 10065, USA.
Andrei S
AS
Kozlov
Daniel
D
Andor-Ardó
A J
AJ
Hudspeth
D000818:Animals; D001001:Anura / Q000502:physiology; D001696:Biomechanical Phenomena / Q000502:physiology; D004058:Diffusion; D004423:Ear / Q000502:physiology*; D055119:Elastic Modulus / Q000502:physiology; D004548:Elasticity / Q000502:physiology*; D006198:Hair Cells, Auditory / Q000502:physiology / Q000648:ultrastructure; D015640:Ion Channel Gating; D016014:Linear Models; D040542:Mechanotransduction, Cellular / Q000502:physiology*; D008954:Models, Biological; D009038:Motion; D012444:Saccule and Utricle / Q000648:ultrastructure; D013696:Temperature; D014783:Viscosity