Thalamic projections of spinothalamic pathways in monkey

The results indicate that the spinothalamic systems of monkey are comprised of pathways through which an area to point relationship exists between the opposite side of the body and the ventrobasal complex, and of diffuse projections which carry input from wide areas of body surface to nuclei adjacent to the vents.

Abstract

The thalamic distribution of peripherally initiated sensory activity which ascends through the ventrolateral fasciculus of the spinal cord has been studied in monkeys in which the dorsal columns had been sectioned. Evoked unitary discharges were routinely recorded from the external segment of the ventrobasal complex in these animals following stimulation of discrete portions of the body. Evidence was obtained which indicated that this spinothalamic projection is somatotopically organized with reference to the body surface. Other thalamic nuclei from which evoked responses were recorded included cell groups of internal medullary lamina and the centrum medianum. Unitary potentials or multiunit recordings from these other responsive zones were found to be evoked by inputs stemming from large, frequently bilateral areas of the body. In addition, nuclei were also shown to respond which were homologous to some of those comprising the posterior nuclear group in cat. The active points in the posterior region also did not show a somatotopic arrangement of the ventrobasal type and were initiated by stimulation of bilateral peripheral inputs. In two instances, responses were also recorded in the external medullary lamina. These results indicate that the spinothalamic systems of monkey are comprised of pathways through which an area to point relationship exists between the opposite side of the body and the ventrobasal complex, and of diffuse projections which carry input from wide areas of body surface to nuclei adjacent to the ventrobasal complex.