The rostral projection of small diameter primary afferents in Lissauer's tract

The rostral projection of A delta and C primary afferents in Lissauer's tract (LT) was studied by assessing how far, rostrally, axons entering at a given level could be activated by electrical stimulation. Sural A delta primary afferents in LT exhibited a rostral projection at least as far as the L3/L4 border, 4 segments rostral to their segment of entry (S1 dorsal root). C-fibers from the sural nerve projected in LT less than 2 segments rostral to their segment of entry. It is concluded that small afferent fibers can project appreciable distances along the spinal cord to bring them into regions not normally responsive to natural stimulation of the receptive field of such fibers.