Variations in vibrissal geometry across the rat mystacial pad: base diameter, medulla, and taper

Abstract

Many rodents tactually sense the world through active motions of their vibrissae (whiskers), which are regularly arranged in rows and columns (arcs) on the face. The present study quantifies several geometric parameters of rat whiskers that determine the tactile information acquired. Findings include the following. ) A meta-analysis of seven studies shows that whisker base diameter varies with arc length with a surprisingly strong dependence on the whisker's row position within the array.) The length of the whisker medulla varies linearly with whisker length, and the medulla's base diameter varies linearly with whisker base diameter. ) Two parameters are required to characterize whisker "taper": radius ratio (base radius divided by tip radius) and radius slope (the difference between base and tip radius, divided by arc length). A meta-analysis of five studies shows that radius ratio exhibits large variability due to variations in tip radius, while radius slope varies systematically across the array.) Within the resolution of the present study, radius slope does not differ between the proximal and distal segments of the whisker, where "proximal" is defined by the presence of the medulla. ) Radius slope of the medulla is offset by a constant value from radius slope of the proximal portion of the whisker. We conclude with equations for all geometric parameters as functions of row and column position. Rats tactually explore their world by brushing and tapping their whiskers against objects. Each whisker's geometry will have a large influence on its mechanics and thus on the tactile signals the rat obtains. We performed a meta-analysis of seven studies to generate equations that describe systematic variations in whisker geometry across the rat's face. We also quantified the geometry of the whisker medulla. A database provides access to geometric parameters of over 500 rat whiskers.

Effects of Multi-Point Contacts during Object Contour Scanning Using a Biologically-Inspired Tactile Sensor

“…Returning to the biological paragon, animal's vibrissae show some geometrical features, which are neglected in the present paper. In particular, they are rather tapered and pre-curved than cylindrically shaped, as considered here [22,23]. It can be assumed, that MPCs along a tapered rod would cause more pronounced kinks, than observed in the present work.…”

Three-dimensional contact point determination and contour reconstruction during active whisking behavior of the awake rat

“…It is reasonable to assume that almost all naturally occurring whiskers will be tapered [40–43], be largely (but not entirely) planar [44, 45], and have a curvature that is mostly well-described by either a quadratic or cubic equation [44–46]. Trimming the tip of the whisker, as might occur through natural damage or barbering, would have no effect on mapping uniqueness.…”

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

“…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.…”

“…We tested ( Figure 2B, lower panel) whether the simulations using optimized parameters would generalize to explain the dynamics of all whiskers within the average whisker array as described by the equations found in Belli et al (40). The simulations identical to those described in section 4.5.1, but all 28 whiskers comprising the right side of the array (rows A-E, columns Greek-5) were simulated.…”

“…The resonance frequencies from Neimark et al (34) was obtained from Table 1 of the article (Pulse mode experiment). Because whisker arc length was not published for these data, we used average values from Belli et al (40) for the corresponding whisker identities (β, C1, C2, C3, C4).…”