Pyramidal and Non-Pyramidal Pathways in Monkeys: Anatomical and Functional Correlation

In monkeys, corticospinal fibers terminate on motoneurons and interneurons. Brainstem fibers, which may be grouped into medial and lateral pathways, terminate on the same interneurons. Observations following bilateral pyramidotomy indicate that motility can be adequately directed by the brainstem systems while cortical connections add speed and the capacity for further fractionating movements. Further experiments suggest that the medial and lateral brainstem pathways primarily direct proximal and distal movements, respectively.