title: Beyond cones: an improved model of whisker bending based on measured mechanics and tapering.
abstract: The sense of touch is represented by neural activity patterns evoked by mechanosensory input forces. The rodent whisker system is exceptional for studying the neurophysiology of touch in part because these forces can be precisely computed from video of whisker deformation. We evaluate the accuracy of a standard model of whisker bending, which assumes quasi-static dynamics and a linearly tapered conical profile, using controlled whisker deflections. We find significant discrepancies between model and experiment: real whiskers bend more than predicted upon contact at locations in the middle of the whisker and less at distal locations. Thus whiskers behave as if their stiffness near the base and near the tip is larger than expected for a homogeneous cone. We assess whether contact direction, friction, inhomogeneous elasticity, whisker orientation, or nonconical shape could explain these deviations. We show that a thin-middle taper of mouse whisker shape accounts for the majority of this behavior. This taper is conserved across rows and columns of the whisker array. The taper has a large effect on the touch-evoked forces and the ease with which whiskers slip past objects, which are key drivers of neural activity in tactile object localization and identification. This holds for orientations with intrinsic whisker curvature pointed toward, away from, or down from objects, validating two-dimensional models of simple whisker-object interactions. The precision of computational models relating sensory input forces to neural activity patterns can be quantitatively enhanced by taking thin-middle taper into account with a simple corrective function that we provide.
authors.affiliation: Neurobiology Section, Department of Biological Sciences, University of Southern California, Los Angeles, California; shires@usc.edu.
authors.forename: Samuel Andrew
authors.identifier: 0000-0003-3498-0388
authors.initials: SA
authors.lastname: Hires
authors.affiliation: Neurobiology Section, Department of Biological Sciences, University of Southern California, Los Angeles, California;
authors.forename: Adam
authors.initials: A
authors.lastname: Schuyler
authors.affiliation: Neurobiology Section, Department of Biological Sciences, University of Southern California, Los Angeles, California;
authors.forename: Jonathan
authors.initials: J
authors.lastname: Sy
authors.affiliation: Neurobiology Section, Department of Biological Sciences, University of Southern California, Los Angeles, California;
authors.forename: Vincent
authors.initials: V
authors.lastname: Huang
authors.affiliation: Neurobiology Section, Department of Biological Sciences, University of Southern California, Los Angeles, California;
authors.forename: Isis
authors.initials: I
authors.lastname: Wyche
authors.affiliation: Neurobiology Section, Department of Biological Sciences, University of Southern California, Los Angeles, California;
authors.forename: Xiyue
authors.initials: X
authors.lastname: Wang
authors.affiliation: Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, Virginia; and Department of Physiology and Cell Biology, Department of Physics, and Zlotowski Center for Neuroscience, Faculty of Health Sciences, Ben Gurion University, Be'er-Sheva, Israel.
authors.forename: David
authors.initials: D
authors.lastname: Golomb
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D003198:Computer Simulation; D005260:Female; D007839:Functional Laterality; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D023421:Models, Animal; D009068:Movement / Q000502:physiology*; D017711:Nonlinear Dynamics; D010812:Physical Stimulation; D014110:Touch / Q000502:physiology*; D014738:Vibrissae / Q000033:anatomy & histology / Q000294:innervation / Q000502:physiology*
keywords: mechanics; quasi-static model; somatosensation; stiffness; whisker bending