Miki Ohgushi

Neuronal activity in the monkey fronto-opercular and adjacent insular/prefrontal cortices during a taste discrimination GO/NOGO task: response to cues

The neural coding of taste information in the fronto-opercular cortex (Fop) and the orbitofrontal area (OFA) was investigated by recording neural activities in monkeys performing a NaCl-water discrimination GO/NOGO task. Responses to GO (NaCl) and NOGO cues (water) were recorded from 160 neurons, of which 118 differentially responded to two cues (differential, Dif neurons), and 42 showed the same response (non-differential, ND neurons). Differential neurons included equal numbers of GO- and NOGO-dominant subtypes. Dif and ND neurons may code for different cues, e.g., taste and touch, as shown by our previous study [Jpn. J. Physiol. 44 (1994) 141]. The response latency of neurons in the exposed Fop was distributed with two modes, one at the shortest bin (100 ms) and one at the bin of 400-800 ms, but neurons in the buried Fop and OFA all had long latency. Such a difference between the two cortical groups of neurons suggests different roles in taste discrimination tasks. Most neurons did not show changes in the discharges or latency with varying concentrations of NaCl. The results indicate that neurons in the areas surveyed code for taste information differently in the task-performing state compared with the non-behaving state examined in previous studies.

Differential development of cortical taste areas in granular and dysgranular insular cortices in rats.

Recordings were made from taste neurons in granular and dysgranular areas of the insular cortex of anesthetized SD-rats from the age of 4 days to over 90 days (adults). Almost all of the taste neurons were detected in the dysgranular area prior to weaning, but the number in the granular area increased with age and exceeded the number in the dysgranular area after the age of 50 days. In the dysgranular area, most taste neurons, irrespective of the postnatal age, were located at layer 5. However, in the granular area they were found at a deeper layer, with the advance in age; e.g. layer 2-3 at 14-20 days to layer 5 in adults. Thus, taste afferents in granular and dysgranular areas of the insular cortex differ with advance in age.

Neurons associated with behavioral context errors in the primary and higher-order gustatory cortices in the monkey

Cue responses of neurons in the taste-related cortex of Japanese macaque monkeys were studied during a NaCl-water discrimination GO-NOGO task, to compare the correct and incorrect responses. Most neurons produced a steady pattern of discharges in response to a given cue at both correct and incorrect responses, presumably responding to the physicochemical nature of the cue. Some neurons showed the discharge pattern for a certain cue changing to that for another cue at task error, presumably representing the subsequent behavioral reaction or behavioral context. These neurons were mainly located in the precentral operculum and orbitofrontal cortex, and rarely in the primary gustatory area, area G.

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.