Taking the next step: cortical contributions to the control of locomotion.

The planning and execution of both discrete voluntary movements and visually guided locomotion depends on the contribution of multiple cortical areas. In this review, we discuss recent experiments that address the contribution of the posterior parietal cortex (PPC) and the motor cortex to the control of locomotion. The results from these experiments show that the PPC contributes to the planning of locomotion by providing an estimate of the position of an animal with respect to objects in its path. In contrast, the motor cortex contributes primarily to the execution of gait modifications by modulating the activity of groups of synergistic muscles active at different times during the gait cycle.