Dynamic cues for whisker-based object localization: An analytical solution to vibration during active whisker touch

Abstract

Vibrations are important cues for tactile perception across species. Whisker-based sensation in mice is a powerful model system for investigating mechanisms of tactile perception. However, the role vibration plays in whisker-based sensation remains unsettled, in part due to difficulties in modeling the vibration of whiskers. Here, we develop an analytical approach to calculate the vibrations of whiskers striking objects. We use this approach to quantify vibration forces during active whisker touch at a range of locations along the whisker. The frequency and amplitude of vibrations evoked by contact are strongly dependent on the position of contact along the whisker. The magnitude of vibrational shear force and bending moment is comparable to quasi-static forces. The fundamental vibration frequencies are in a detectable range for mechanoreceptor properties and below the maximum spike rates of primary sensory afferents. These results suggest two dynamic cues exist that rodents can use for object localization: vibration frequency and comparison of vibrational to quasi-static force magnitude. These complement the use of quasi-static force angle as a distance cue, particularly for touches close to the follicle, where whiskers are stiff and force angles hardly change during touch. Our approach also provides a general solution to calculation of whisker vibrations in other sensing tasks.

Whisker Vibrations and the Activity of Trigeminal Primary Afferents in Response to Airflow

“…In touch, however, only those touched whiskers will vibrate. A number of parameters, including the whisker's intrinsic dynamics, the contact location along the whisker length, stick-slip, friction, and object surface texture, affect its vibration frequencies (Ritt et al, 2008;Wolfe et al, 2008;Boubenec et al, 2012;Quist et al, 2014;Vaxenburg et al, 2018). Additionally, as the whisker increasingly deflects against an object, these touch-induced vibrations will damp out (Boubenec et al, 2012;Quist et al, 2014;Hobbs et al, 2016).…”

WHISKiT Physics: A three-dimensional mechanical model of the rat vibrissal array

“…Understanding the underlying principles of the rat somatosensory pathway therefore cannot rely on modeling the sensors of an individual rat in detail (65). Although existing single-whisker models may be able to predict the dynamics of individual whiskers more accurately (32,38,51), the present model has been validated to generate reasonable approximations of real whisker dynamics, well within the naturally occurring variability within and across animals. The present model can be viewed as a "prototypical" rat, whose parameters and dynamics fall within the range of biological rats.…”

“…Mechanical responses of isolated whiskers have been quantified in various contexts (33,40,43,(47)(48)(49)(50)(51)(52)(53), but models of the vibrissal system have typically been quasi-static, two-dimensional (2D), and limited to a single whisker (32,34,38,42,44,(54)(55)(56)(57)(58)(59)(60). These are significant limitations when studying neural circuitry that has evolved with multiple sensors interacting with a three-dimensional complex world.…”

“…Values of Young's modulus have been reported to fall between 1. 3-7.8 GPa (33)(34)(35)(36)(37), while the damping ratio has been estimated between 0.05 and 0.28 (33,34,38).…”

“…The damping ratio calculated from the kinematic behavior of the whisker is smaller than the optimized value for parameter . This difference is likely attributable to the assumption that the damping ratio is uniform along the whisker, as previous studies have suggested that the damping ratio decreases from base to tip (32,33,38). Matching material properties between simulation and experiment does not guarantee that simulated dynamics will accurately match experimental data.…”