The detailed somatotopic organization of the dorsal horn in the lumbosacral enlargement of the cat spinal cord.

The somatotopic organization of spinocervical tract cells and unidentified dorsal horn neurons that lie in the same depth range as the spinocervical tract cells has been examined in detail in the lumbosacral enlargement of cats anesthetized with alpha-chloralose. Only gentle hair movement or light touch of glabrous skin were used as stimuli. Within the region of the dorsal horn containing these neurons there is a precise somatotopic organization. However, there is considerable variation between animals in the relationship between the somatotopic map and the lumbosacral segmental boundaries. The somatotopic map described here is considered to be restricted to a 300- to 500-micron thick lamina. In the medial half to two-thirds of this lamina in the L6 and L7 segments the toes are represented in a rostrocaudal sequence from toe 2 to toe 5. Over the most medial 200-500 micron of this part of the dorsal horn are found cells that respond to stimulation of the glabrous skin of the toe pads and the central pad. The toe representation is surrounded by a strip of foot representation, which is in turn surrounded by a strip of leg representation. The most lateral part of the lamina curves ventrally in the L6 and L7 segments and contains a continuous rostrocaudal representation of the skin of the thigh. In this region are found both spinocervical tract cells and unidentified dorsal horn neurons with receptive fields on the thigh. The skin of the hindlimb is represented such that a line of discontinuity runs down the posteromedial thigh, leg, and foot. Skin lateral to this line is represented caudally, while skin medial to it is represented rostrally.