VISCEROSOMATIC NEURONS IN THE PRIMARY SOMATOSENSORY CORTEX (SI) OF THE SQUIRREL-MONKEY

Thirty-eight neurons in the primary somatosensory cortex (SI) in alpha -chloralose/Nembutal, or halothane (in N2O/O-2) anesthetized squirrel monkeys were tested for responses to distention of the urinary bladder , the distal colon and the lower esophagus. Of the 38 SI neurons studi ed 13 were classified as visceroceptive. Eight of the 13 visceroceptiv e neurons responded to stimulation of a single viscus, the other five responded to two viscera. All SI neurons investigated had somatic low threshold type responses. Anesthesia was a critical factor, because 6 of 11 neurons responded to visceral stimulation only under a light hal othane anesthetic level, and during moderate halothane anesthesia leve ls significantly more neurons exhibited visceral inputs than under alp ha-chloralose/Nembutal. The results suggest that the squirrel monkey S I is involved in processing of visceral information.