Proprioceptive pathways of the spinal cord.

In the Macaque, surgical lesions were made in the dorsal funiculus, in the dorsolateral funiculus, and through half of the spinal cord. The somatosensory and motor capacity of the animal were examined neurologically and electrophysiologically. The exact lesion was then confirmed pathologically in detail. The results of these experiments indicate that limb position information from the distal limb and proximal limb are relayed to the brain in two different fashions. Distal limb position information, especially the cortical representation of the limbs' volar surface as it moves in space, is drastically impaired by dorsal funiculus or posterior white column lesions. Proximal limb position may or may not be impaired by similar lesions, for this information while initially in the dorsal or posterior white columns is sorted out (as it ascends in the spinal cord) to the dorsolateral funiculus or white columns. For example, in the lower thoracic spinal cord, both distal and proximal hind limb sensation are impaired by posterior white column damage; in the cervical cord, only distal sensation is impaired by the same lesion, and proximal information is spared. We refer to this neuroanatomic rearranging as "fibre sorting", and we believe that it is clinically significant in spinal cord disease.