title: Porosity controls spread of excitation in tectorial membrane traveling waves.
abstract: Cochlear frequency selectivity plays a key role in our ability to understand speech, and is widely believed to be associated with cochlear amplification. However, genetic studies targeting the tectorial membrane (TM) have demonstrated both sharper and broader tuning with no obvious changes in hair bundle or somatic motility mechanisms. For example, cochlear tuning of Tectb(-/-) mice is significantly sharper than that of Tecta(Y1870C/+) mice, even though TM stiffnesses are similarly reduced relative to wild-type TMs. Here we show that differences in TM viscosity can account for these differences in tuning. In the basal cochlear turn, nanoscale pores of Tecta(Y1870C/+) TMs are significantly larger than those of Tectb(-/-) TMs. The larger pore size reduces shear viscosity (by ∼70%), thereby reducing traveling wave speed and increasing spread of excitation. These results demonstrate the previously unrecognized importance of TM porosity in cochlear and neural tuning.
authors.affiliation: Harvard-Massachusetts Institute of Technology Division of Health Sciences and Technology, Cambridge, Massachusetts; Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts.
authors.forename: Jonathan B
authors.initials: JB
authors.lastname: Sellon
authors.affiliation: Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts.
authors.forename: Roozbeh
authors.initials: R
authors.lastname: Ghaffari
authors.affiliation: Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts; Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts.
authors.forename: Shirin
authors.initials: S
authors.lastname: Farrahi
authors.affiliation: Sussex Neuroscience, School of Life Sciences, University of Sussex, Falmer, Brighton, United Kingdom.
authors.forename: Guy P
authors.initials: GP
authors.lastname: Richardson
authors.affiliation: Harvard-Massachusetts Institute of Technology Division of Health Sciences and Technology, Cambridge, Massachusetts; Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts; Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts. Electronic address: freeman@mit.edu.
authors.forename: Dennis M
authors.initials: DM
authors.lastname: Freeman
mesh_terms: D000818:Animals; D016326:Extracellular Matrix Proteins / Q000235:genetics / Q000378:metabolism; D058851:GPI-Linked Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D016062:Porosity; D013680:Tectorial Membrane / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology; D014732:Vibration; D014783:Viscosity
chemical_list: D016326:Extracellular Matrix Proteins; D058851:GPI-Linked Proteins; C105350:Tecta protein, mouse