Response properties of neurons to sucrose in the reward phase and the areal distribution in the monkey fronto-operculuro-insular and prefrontal cortices during a taste discrimination GO/NOGO task

The neural activities to sucrose in the reward phase were examined in the primate fronto-operculo-insular and prefrontal cortices during a NaCl-water discrimination GO/NOGO task. Neurons were classified according to the cue-responsiveness into sucrose-specific, cue-differential, or cue-non-differential groups. The onset latencies and decay times divided response temporal patterns into four types. All cue-non-differential neurons were the short latency-short decay type, whereas most sucrose-specific and cue-differential neurons were either the short latency-short decay or short latency-long decay type. Most neurons were histologically located in areas G, 3, and 1-2, the primary gustatory cortices (PGCs), and the precentral operculum, one of the higher-order gustatory cortices (HGCs), whereas a few were in other HGCs, e.g., area 12. Further study of the temporal properties of the neurons in each cortical area revealed two subgroups of short-latency responses with different onset latencies and a group of responses with an intermediate decay time around the boundary between short- and long-decay times in the PGCs. The onset latencies to cues and sucrose were significantly correlated in the HGC, but not in the PGC. These results indicate that different processing mechanisms operate for sucrose in the reward phase in the PGC and HGC.