title: Two-Dimensional Cochlear Micromechanics Measured In Vivo Demonstrate Radial Tuning within the Mouse Organ of Corti.
abstract: The exquisite sensitivity and frequency discrimination of mammalian hearing underlie the ability to understand complex speech in noise. This requires force generation by cochlear outer hair cells (OHCs) to amplify the basilar membrane traveling wave; however, it is unclear how amplification is achieved with sharp frequency tuning. Here we investigated the origin of tuning by measuring sound-induced 2-D vibrations within the mouse organ of Corti in vivo Our goal was to determine the transfer function relating the radial shear between the structures that deflect the OHC bundle, the tectorial membrane and reticular lamina, to the transverse motion of the basilar membrane. We found that, after normalizing their responses to the vibration of the basilar membrane, the radial vibrations of the tectorial membrane and reticular lamina were tuned. The radial tuning peaked at a higher frequency than transverse basilar membrane tuning in the passive, postmortem condition. The radial tuning was similar in dead mice, indicating that this reflected passive, not active, mechanics. These findings were exaggerated in Tecta(C1509G/C1509G) mice, where the tectorial membrane is detached from OHC stereocilia, arguing that the tuning of radial vibrations within the hair cell epithelium is distinct from tectorial membrane tuning. Together, these results reveal a passive, frequency-dependent contribution to cochlear filtering that is independent of basilar membrane filtering. These data argue that passive mechanics within the organ of Corti sharpen frequency selectivity by defining which OHCs enhance the vibration of the basilar membrane, thereby tuning the gain of cochlear amplification.
  
  
  
  Outer hair cells amplify the traveling wave within the mammalian cochlea. The resultant gain and frequency sharpening are necessary for speech discrimination, particularly in the presence of background noise. Here we measured the 2-D motion of the organ of Corti in mice and found that the structures that stimulate the outer hair cell stereocilia, the tectorial membrane and reticular lamina, were sharply tuned in the radial direction. Radial tuning was similar in dead mice and in mice lacking a tectorial membrane. This suggests that radial tuning comes from passive mechanics within the hair cell epithelium, and that these mechanics, at least in part, may tune the gain of cochlear amplification.
authors.affiliation: E.L. Ginzton Laboratory and Department of Electrical Engineering, Stanford University, Stanford, California 94305.
authors.forename: Hee Yoon
authors.initials: HY
authors.lastname: Lee
authors.affiliation: Department of Otolaryngology-Head and Neck Surgery, Stanford University, Stanford, California 94305, and.
authors.forename: Patrick D
authors.initials: PD
authors.lastname: Raphael
authors.affiliation: Department of Otolaryngology-Head and Neck Surgery, Stanford University, Stanford, California 94305, and.
authors.forename: Anping
authors.identifier: 0000-0003-2530-6375
authors.initials: A
authors.lastname: Xia
authors.affiliation: Department of Otolaryngology-Head and Neck Surgery, Stanford University, Stanford, California 94305, and.
authors.forename: Jinkyung
authors.initials: J
authors.lastname: Kim
authors.affiliation: Department of Otolaryngology-Head and Neck Surgery, Stanford University, Stanford, California 94305, and.
authors.forename: Nicolas
authors.identifier: 0000-0001-8007-9246
authors.initials: N
authors.lastname: Grillet
authors.affiliation: Department of Biomedical Engineering, Texas A&M University, College Station, Texas 77843.
authors.forename: Brian E
authors.initials: BE
authors.lastname: Applegate
authors.affiliation: E.L. Ginzton Laboratory and Department of Electrical Engineering, Stanford University, Stanford, California 94305.
authors.forename: Audrey K
authors.identifier: 0000-0002-5412-3976
authors.initials: AK
authors.lastname: Ellerbee Bowden
authors.affiliation: Department of Otolaryngology-Head and Neck Surgery, Stanford University, Stanford, California 94305, and joghalai@stanford.edu.
authors.forename: John S
authors.identifier: 0000-0003-4241-6189
authors.initials: JS
authors.lastname: Oghalai
mesh_terms: D000161:Acoustic Stimulation / Q000379:methods*; D000818:Animals; D003198:Computer Simulation; D005260:Female; D008297:Male; D040542:Mechanotransduction, Cellular / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008959:Models, Neurological; D009925:Organ of Corti / Q000502:physiology*; D010898:Pitch Perception / Q000502:physiology*; D011312:Pressure; D033081:Shear Strength / Q000502:physiology; D013680:Tectorial Membrane / Q000502:physiology*; D014732:Vibration
keywords: auditory system; cochlea; frequency discrimination; hearing; mechanics; transduction