Search

The ascending degeneration resulting from experimental lesions of the ventral funiculus of the spinal cord of Macaca mulatta has been studied using the Nauta technique and its variants. The ventral spinothalamic tract is shown to be an independent entity with respect to the lateral spinothalamic tract; its fibers are widely distributed in the ventral funiculus and it establishes connections with the brain stem and thalamus which are analogous but not identical to those of the latter. Its role in the relay of nociceptive input is discussed in view of the similarity in hodology of the two systems and it is proposed that it may be responsible for the failure of anterolateral cordotomy to control pain on a long term basis. Other ascending systems in the ventral funiculus include the spino-olivary and spino-reticular tracts, as well as minor connections to the N. of Edinger-Westphal, the red nucleus and the superior colliculus. The projections from the ventral quadrant of the spinal cord to the brain stem are almost entirely ipsilateral until the rostral mesencephalon is reached, at which level the N. of Darkschewitz receives both ipsilateral and crossed input; the magnocellular nucleus of the medial geniculate body receives a small contribution which is mainly ipsilateral. In the thalamus the VPL receives predominantly ipsilateral projections while the input to the paralaminar nuclei is only slightly less pronounced contralaterally than ipsilaterally.

In the same year in which Gowers wrote the prophetic statement quoted above, Bechterew on the basis of mylogenetic studies described two ascending fibre systems in the anterolateral funiculus of the spinal cord, two systems that were directly continuous into the reticular formation of the brain-stem. These two pathways consisted of a medial “ground bundle” of the lateral funiculus and a more lateral system of “the rest of the lateral funiculus,” exclusive of the dorsal spinocerebellar tract of Flechsig (text-fig. 1).

HIGH-THRESHOLD MECHANORECEPTORS and their centrally projecting myelinated fibers make up a functionally distinct group of cutaneous sensory units that have been suggested as part of the afferent apparatus for pain resulting from mechanical damage to the skin (3, 17). The argument for their relation to pain was based on two points: 1) the ability of such afferent elements, unique among those with medullated fibers, to provide signals differentiating noxious from innocuous mechanical events affecting the skin; and 2) the well-established correlation between pain and activity in thin myelinated afferent fibers