Two distinct projection areas from tongue nerves in the frontal operculum of macaque monkeys as revealed with evoked potential mapping.

Projection areas in the cerebral cortex from tongue nerves were investigated in anesthetized macaque monkeys (Macaca fuscata). Three tongue nerves (lingual nerve, chorda tympani, and a lingual branch of the glossopharyngeal nerve) were electrically stimulated and thereby evoked mass field potentials were recorded with microelectrodes roving through the exposed and buried frontal operculum. Two distinct tongue nerve projection areas were thus located; one in the lower part of the precentral gyrus ventral to the inferior precentral sulcus, and the other in the medial part of the buried frontal operculum. The former corresponds to the "cortical masticatory area", previously defined in macaque monkeys as involved in somatic sensation as well as mastication. However, the prominent projection from the chorda tympani and glossopharyngeal nerve branch, containing taste fibers, to this area suggests its involvement in taste sensation. The latter corresponds to the "pure gustatory area" defined in squirrel monkeys in both location and cytoarchitecture. However, projection to this area from the lingual nerve, which contains only somatic nerve fibers, suggests its involvement in somatic sensation, as well.