Whisking control by motor cortex

The rodent whiskers (the so-called vibrissae) are an active scanning sensorimotor system with major perceptual functions. Apart from tactile perception, the whisker motor system also has important contributions to the animals’ navigation and orientation capabilities. The whisker motor system is highly modular with circuits processing basic motor commands, rhythmic whisking, and modulating the motor actions using information from incoming tactile signals. The vibrissal primary motor cortex (vM1) reflects these functional divisions by displaying a distinct set of sub-areas with different functions. Like the primate fingertip system, vM1 displays direct cortico-motoneurons (CM) cells, in principle compatible with the notion that vM1 is involved in directly computing patterns of muscle activity. There is strong evidence, however, that vM1 action on the muscles is rather indirect with important brainstem premotor networks bearing the responsibility of computing muscle activity patterns. The connectivity of the different vM1 modules to central pattern generators (CPGs), generating the basic rhythmic movement patterns and the trigeminal brainstem loop (TBL), the brainstem sensorimotor reflex arc, representing the lowest hierarchy of sensorimotor interactions, are being unearthed by current investigations.