Longitudinal spread of mechanical excitation through tectorial membrane traveling waves

Jonathan B. Sellon, Shirin Farrahi, Roozbeh Ghaffari, Dennis M. Freeman*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

26 Scopus citations


The mammalian inner ear separates sounds by their frequency content, and this separation underlies important properties of human hearing, including our ability to understand speech in noisy environments. Studies of genetic disorders of hearing have demonstrated a link between frequency selectivity and wave properties of the tectorial membrane (TM). To understand these wave properties better, we developed chemical manipulations that systematically and reversibly alter TM stiffness and viscosity. Using microfabricated shear probes, we show that (i) reducing pH reduces TM stiffness with little change in TM viscosity and (ii) adding PEG increases TM viscosity with little change in TM stiffness. By applying these manipulations in measurements of TM waves, we show that TM wave speed is determined primarily by stiffness at low frequencies and by viscosity at high frequencies. Both TM viscosity and stiffness affect the longitudinal spread of mechanical excitation through the TM over a broad range of frequencies. Increasing TM viscosity or decreasing stiffness reduces longitudinal spread of mechanical excitation, thereby coupling a smaller range of best frequencies and sharpening tuning. In contrast, increasing viscous loss or decreasing stiffness would tend to broaden tuning in resonance- based TMmodels. Thus, TM wave and resonance mechanisms are fundamentally different in the way they control frequency selectivity.

Original languageEnglish (US)
Pages (from-to)12968-12973
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number42
StatePublished - Oct 20 2015


  • Cochlear mechanics
  • Resonance
  • Tectorial membrane
  • Traveling waves
  • Viscoelastic materials

ASJC Scopus subject areas

  • General


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