Many of the projections derive from both sensory and motor cortex and synapse upon dorsal horn neurons which in turn project to the motor neurons within the ventral horn. The development of the corticospinal tract is the greatest in humans, where cortical neurons exert a profound direct innervation of the motor neurons. The most dramatic example of how this organization is reflected functionally is in the consequences of disruption of the corticospinal tracts. In humans this leads to a total loss of voluntary movement, while lower primates retain the ability to maintain posture and even climb although they lose the ability to grasp and manipulate objects. In contrast, lesions of the precentral gyrus lead to a temporary paralysis.
Recovery is dependent on the development of corticospinal synaptic synapses.
As in the somatosensory system, area 4 exhibits a topographical organization with neurons involved in activating the lower limbs found medially, and neurons innervating the motor neurons activating the upper limbs more laterally. Area 6 also regulates motor activity, particularly in the initiation of movement. Area 6 projects to area 4 to initiate movement. These areas are important in the planning of movement. In rodents the division is not as clear.