AFFERENT PROJECTIONS THROUGH VENTROLATERAL FUNICULI TO THALAMUS OF CAT

Abstract

The thalamic termination of pathways traversing the ventrolateral funiculi of the spinal cord was investigated in anesthetized cats which had sustained prior surgical destruction of both dorsal funiculi at a spinal level rostral to the entrance of the peripheral inputs. Electrical stimulation of cutaneous nerves in each of the 4 limbs was found to evoke electrical activity in 2 regions of the thalamus. One of these regions comprised the known primary relay nuclei for somesthetic sensation, the ventrobasal complex. The activity elicited in the ventrobasal complex by cutaneous nerve stimulation was obtained predominantly from contralateral inputs after latencies approximating those reported in intact animals, and exhibited the previously described patterns of somatotopic organization. The 2d responsive region was situation caudad and mediad to the ventrobasal complex and corresponded largely to the posterior nuclear group of the pulvinar-posterior system including the magnocellular division of the medial geniculate body. Evoked activity at a given locus in this posterior region could be recorded following stimulation of both contralateral and ipsilateral cutaneous nerves. The latencies of these evoked responses were frequently longer than those observed for ventrobasal potentials. Little evidence for a somatotopic organization of this region was found. These data provide further information on the relationship between the ventrolateral ascending spinal pathways and thalamic regions which appear to project to the somatosensory areas of the cerebral cortex.