Topography of whisking II: Interaction of whisker and pad

The peripheral effector system mediating rodent whisking produces protraction/ retraction movements of the whiskers and translation movements of the collagenous mystacial pad. To examine the interaction of these movements during whisking in air we used high-resolution, optoelectronic methods for two-dimensional monitoring of whisker and pad movements in head-fixed rats. Under these testing conditions ( 1) whisker movements on the same side of the face are synchronous and of similar amplitude; ( 2) pad movements exhibit the characteristic 'exploratory' rhythm ( 6 - 12 Hz) of whisking but their movements often have a low frequency ( 1 - 2 Hz) component; ( 3) Pad movements occur in both antero-posterior and dorso-ventral planes but there are considerable variations in the amplitude and topography of movement parameters in the two planes. We conclude that ( a) both whisker and pad receive input from a common central rhythm generator; (b) differences in whisker and pad amplitude and topography probably reflect differences in the biomechanical properties of the structures receiving that input; ( c) pad movements make a significant contribution to the kinematics of whisking behavior and (d) the two-dimensional nature of pad translation movements significantly increases the rat's flexible control of its mobile sensor.