Somatotopic representation of hindlimb skin in cat dorsal horn.

Single-unit exploration of the dorsal horn of segments L4-S2 of unanesthetized cats with the neuraxis transected at lower thoracic levels reveals a somototopic organization in the horizontal plane. The dorsal horn dermatomes correspond closely to the dermatomes of the corresponding dorsal roots, and the ML gradient is equally well described by two different projection schemes: a distoproximal gradient and a ventrodorsal one (5, 33). There is no evidence of segmental discontinuity of the map. As is the case in other nuclear regions of the CNS, the relative area devoted to projections from the foot is disproportionately large relative to the area devoted to skin regions of similar size which are located more proximally on the limb. From our data, and from the close correspondence to anatomical data obtained by others, we suggest that at least some cutaneous afferent fibers from a given skin area project directly to any dorsal horn region where that skin area is represented. This assumption, together with the organization of the dorsal horn map, yields a model which predicts a precise somatotopic organization of presynaptic neuropil in the substantia gelatinosa.