How might the motor cortex individuate movements?

The ability to individuate movements--that is, the ability to move one or more body parts independently of the movement or posture of other contiguous body parts--imparts an increasing flexibility to the motor repertoire of higher mammals. The movements used in walking, grasping, or eating contrast greatly with the phylogenetically more recent movements of the same body parts used, respectively, in dancing, playing a musical instrument, or talking. The movements used in the latter functions depend critically on the primary motor cortex (area 4). With advances in our understanding of the output organization of the motor cortex (reviewed recently by Roger Lemon), which have been based largely on studies of the hand area in primates, we can now consider more fully certain problems inherent in moving body parts individually, and some ways in which the motor cortex might accomplish this feat.