Corticospinal projections originate from the arcuate premotor area

We investigated the patterns of corticospinal projection to different segments of the cervical spinal cord using retrograde transport of wheat germ agglutinin conjugated to horseradish peroxidase. We confirmed prior suggestions that the arcuate premotor area (APA) has a significant projection to the spinal cord. In addition, we observed that the corticospinal projection from the APA terminates in upper, but not lower segments of the cervical spinal cord. Furthermore, the region of the APA which projects to the cervical cord also projects to the arm area of the primary motor cortex on the crest of the precentral gyrus. Thus, we conclude that the APA projection to upper cervical segments is involved in the cortical control of arm movements.