Texture sensation through the fingertips and the whiskers.

Texture sensation in primates, through the fingertips, and in rats, through the whiskers, is rapid and accurate. Recent work has provided enough knowledge to allow comparison of the mechanisms. In primates, coarse textures are sensed through a spatial signal - increasing roughness leads to greater contrast in firing among neurons with nearby receptive fields. Fine textures are sensed by a motion signal - when the fingertip translates across the surface, excitation of rapidly adapting receptors varies according to texture. In rats, passage of a whisker over a surface leads to a motion signal that varies according to roughness. Motion is converted to neuronal spike trains, with progressively rougher surfaces leading to progressively greater firing rates. The extraction of texture by the whiskers shares basic features with the motion-based mechanism in primates. Spatial relationships among whiskers may serve purposes other than texture.