Whisker-mediated texture discrimination

Abstract

Rats use their whiskers to rapidly and accurately measure the texture of objects. The authors evaluate recent evidence about how whisker movement across a surface produces texture-specific motion signals, and how the signals are represented by the brain.

Figure 1. Setup for the Experiment of Wolfe and Colleagues

(A) An optic sensor was placed below the textured plate; the rat palpated the texture with its whiskers. (B) The position of each whisker (red square centered at peak of the whisker shadow) was measured at 4 kHz frame rate and ~5 micron spatial resolution. Adapted from [12].

Figure 2. Whisker Trajectories

Whisker trajectory measured when the whiskers moved through the air with no texture present (upper trace) and when the whiskers contacted texture P1200 (middle trace) and texture P400 (lower trace). Adapted from [12]. Texture photographs from [10].

Figure 3. Comparison of Whisker Motion Profiles Collected under Different Conditions

Kinetic signatures are apparent in position (blue traces) and velocity (green traces), and these are conserved across experimental conditions. (A) Contact of D3 whisker with texture P150, measured ~10 mm from the base (adapted from [12]). (B) Contact of C3 whisker with texture P280 (upper panel) and with texture P100 (lower panel), both measured 1 mm from the base (adapted from [10]).

Figure 4. Candidate Texture-Coding Mechanisms

(A) In two different studies, progressively coarser textures evoked kinetic signatures with higher magnitude kinetic events. Red marks are slip-stick events from [12] measured for whiskers D1 and D2; blue marks are ENL from [10] measured for whisker C3. (B) Higher ENLs led to higher firing rates in the trigeminal ganglion (black diamonds) and barrel cortex (green squares). Adapted from [10]. (C) Texture-specific spike patterns. Peristimulus time histogram (2 ms bins; 100 trials) of a ganglion cell for two whisks on textures P280 (left) and P100 (right). Mean firing rate (dashed red lines) were similar, suggesting temporal firing pattern as a critical coding mechanism.