Neural activities in the fronto-opercular cortex of macaque monkeys during tasting and mastication

We recorded responses from 298 units in the fronto-opercular cortex (Fop) of three Japanese macaque monkeys. The units were activated while animals were drinking or eating. Three types of units could be defined: units with transient responses to the delivery of all the fluid into the mouth (ON-type units; n = 123); units activated in association with certain oral movements, e.g., licking (MO-type units; n = 90); and units responsive specifically to a certain fluid (taste units; n = 85). In both ON-type and MO-type units were included mechanoreceptive units with receptive fields in the oral cavity, mainly on the tongue and teeth. All but two taste units responded exclusively to gustatory stimuli. ON-type units were found mainly in the precentral opercular area (PrCO), and MO-type units were recorded predominantly in PrCO and area 6. Taste units were concentrated at the gustatory area and at a part of area 1-2. These results indicate the lack of convergence of somatic and taste input on single neurons. In awake monkeys, Fop units of a given function tended to be clustered at certain loci, thereby forming separate functional regions.