Viscero-somatic 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/O2) 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 studied 13 were classified as visceroceptive. Eight of the 13 visceroceptive 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 halothane anesthetic level, and during moderate halothane anesthesia levels significantly more neurons exhibited visceral inputs than under alpha-chloralose/Nembutal. The results suggest that the squirrel monkey SI is involved in processing of visceral information.