The search space of the rat during whisking behavior.

Rodents move their vibrissae rhythmically to tactually explore their surroundings. We used a three-dimensional model of the vibrissal array to quantify the rat's 'search space' during whisking. Search space was quantified either as the volume encompassed by the array or as the surface formed by the vibrissal tips. At rest, the average position of the vibrissal tips lies near the rat's mouth, and the tips are all approximately equidistant from the midpoint between the rat's eyes, suggesting spatial registration with the visual system. The intrinsic curvature of the vibrissae greatly increases the volume encompassed by the array, and during a protraction, roll and elevation changes have strong effects on the trajectories of the vibrissal tips. The size of the rat's search space--as measured either by the volume of the array or by the surface area formed by the vibrissal tips--was surprisingly unaffected by protraction angle. In contrast, search space was strongly correlated with the 'spread' of the array, defined as the angle between rostral and caudal-most whiskers. We draw two conclusions: first, that with some caveats, spread can be used as a proxy for changes in search space, and second, in order to change its sensing resolution, the rat must differentially control rostral and caudal vibrissae. Finally, we show that behavioral data can be incorporated into the three-dimensional model to visualize changes in vibrissal search space and sensing resolution during natural exploratory whisking.