Whisker-based discrimination of object orientation determined with a rapid training paradigm.

Rats use their large facial whiskers to discriminate the spatial features of objects. Despite numerous electrophysiological recording studies in the central trigeminal whisker representations that document neurons tuned to the direction of whisker deflection, there is no behavioral evidence to date that rats can use their whiskers to discriminate between object orientations. In the present study, we characterized whisker-dependent orientation discrimination using a one-trial learning procedure. Sprague-Dawley rats were trained and tested in a three-arm 'Y-maze' that was outfitted with 180 independently moveable bars that protruded into the arms of the maze to contact the whiskers. On the first day, the maze was configured to have two arms with only horizontal bars and a third arm with only vertical bars and rats were allowed to freely explore all arms. On the second day, rats were isolated in one arm that contained only vertical bars as a conditioned stimulus (CS) and administered three mild foot shocks. On the third day, the maze was configured identically to the first day and rats were once again allowed to freely explore the maze. We measured the percentage of time spent in each arm of the maze and found that most rats spent significantly less time in the arm containing the CS after training compared to before training. Subsequent control experiments determined that the conditioned avoidance was attributable to orientation cues, was caused by the association of the conditioned and unconditioned stimulus and was whisker-dependent. Avoidance behavior was significantly reduced when the difference between the conditioned and non-conditioned orientation difference was reduced to 45 degrees. Thus, rats can discriminate object orientation with their whiskers and an estimate of their discrimination thresholds can be rapidly acquired through the application of a one-trial learning paradigm.