Cerebral units activated by tactile stimuli via a ventral spinal pathway in monkeys

Extracellular microelectrode recordings were made in the forelimb and/or hindlimb areas of the cerebral post-central gyri of 7 monkeys before and/or after acute dorsal hemisections of the cervical or low thoracic spinal cord. The animals were anaesthetized with either pentobarbitone sodium or chloralose. Among the units which were encountered after the lesions were 114 which could be influenced from the periphery. 38 units discharged to light tactile stimulation of small receptive fields and had a topographical organization like that observed in the intact animal. The remaining 76 units could be activated by peripheral electrical stimulation and/or by tapping, squeezing or light pinching. No units were found which specifically were activated by noxious stimuli. The two groups of cortical units responded with latencies only slightly longer than those obtained in the intact preparation. In the light of previous findings these electrophysiological data suggest that, unlike carnivora, primates may possess the ventral spinal somatosensory pathway traditionally postulated on the basis of neurological material.