Toward behavioral benchmarks for whisker-related sensory processing.

Editor's Note: These short, critical reviews of recent papers in the Journal, written exclusively by graduate students or postdoctoral fellows, are intended to summarize the important findings of the paper and provide additional insight and commentary. For more information on the format and purpose of the Journal Club, please see The rodent whisker-to-barrel pathway serves as a major model system for the investigation of sensorimotor processing. Its key advantage is a well defined topographic map, in which each of the orderly arranged whiskers on the snout of the animal is processed largely in a corresponding functional column in primary somatosensory (" barrel ") cortex. This topographic map is situated on top of a lissencephalic cortex, and is thus easily accessible for electrodes or imaging microscopes. The map can be easily altered , e.g., by plucking whiskers during different stages of brain development, allowing study of plasticity mechanisms. Furthermore , rodents use their whiskers for exploration in a highly active manner, rhythmically sweeping them back and forth (" whisking "), which provides the opportunity to study sensorimotor integration in a system with considerably fewer degrees of freedom than primate hands. Although barrel cortex is well described in terms of microcircuitry (Lübke and Feldmeyer, 2007) and mechanisms of plasticity (Feldman and Brecht, 2005), there is a paucity of behavioral data on whisker usage. While rats clearly can use their whiskers for object localization (Hutson and Masterton, 1986) and texture discrimination (Carvell and Simons, 1990), little is known about how the animals employ their whiskers to accomplish these tasks. This situation is largely because of a lack of methods that allow precise quantification of whisker movements while, at the same time, permitting psychophysical assessments. The intricate interplay of whiskers and surfaces during free exploration calls for analysis with millisecond resolution and microme-ter precision and can most accurately be examined using high-speed videography, which in turn requires sophisticated analysis software to track single whiskers (Ritt et al., 2008). Because of the lack of psychophysical whisker-based paradigms and the difficulties in measuring whisking, experiments and theories on whisker sensory processing have been largely unconstrained by behav-ioral benchmarks. For example, investigators have routinely stimulated whiskers with amplitudes and velocities that have recently been found to be on the lower end of the spectrum rats encounter during exploration (Ritt et al., 2008) and, in fact, are occasionally close to absolute perceptual threshold (Stüttgen et al., 2006). Similarly, …