Foods Food Ingredients J. Jpn., Vol. 212, No.9, 2007
Gustatory Discrimination Behavior and Neuronal Activity in the Gustatory Cortex of
Primates
Hisashi Ogawa a), Hirotoshi Ifuku b), Miki Ohgushi c), Tamio Nakamura d), Shin-ichi Hirata e)
a) Juryo Group Kumamoto Kinoh Hospital
6-8-1, Yamamuro, Kumamoto 860-8518, Japan
b) Faculty of Education, Kumamoto University
2-40-1, Kurokami, Kumamoto 860-8555, Japan
c) Department of Rehabilitaion, Kumamoto University Hospital
1-1-1, Honjo, Kumamoto 860-8556, Japan
d) National Kikuti Hospital
208, Fukuhara, Koshi-shi, Kumamoto 861-1116, Japan
e) Department of Psychiatry and Neuropathobiology, Kumamoto University Hospital
1-1-1, Honjo, Kumamoto 860-8556, Japan
Summary
Two types of NaCl-water discrimination GO/NOGO tasks, a reaction time task and a delayed task
with task reversal, were developed to investigate differential involvement of the primary and
higher-order gustatory cortices in gustatory information processing in primates. In a reaction time
task, NaCl was a GO cue and water was a NOGO cue. Monkeys were asked to press a lever as soon
as possible when they tasted salty in response to fluid delivered to their mouth but not to do it
when they tasted only water. When they behaved correctly, they received sucrose as a reward. In a
delayed task with task reversal, a monkey had to press a lever during the time period when a LED
was turned on, and the relationship between kinds of cues and task behavior was changed during
the task without warning. During performance of the task, neuronal activities were recorded from
the primary and higher-order gustatory cortices in monkeys, and the following findings were
obtained.
In the reaction time task, most neurons differentially yielded ON type responses to GO or NOGO
cues in either primary or higher-order cortices. They did not increase the magnitude of responses
to the GO cue (NaCl) with the increase of GO intensity (NaCl concentration) nor change response
latencies with the GO intensity. In the delayed task, most neurons in the primary gustatory
cortices yielded consistent responses to cues with the same chemical nature in spite of task
reversal, whereas those in higher-order cortices produced consistent responses to GO or NOGO
cues in spite of changes in the chemical nature. The higher-order cortices contain neurons involved
in working memory or preparation of task behavior. On the other hand, a few types of reward
responses with different onset latencies, as expected from the peripheral taste fibers, were noted in
the reaction time task, but several types of reward responses were found in the delayed task
including responses representing correct or incorrect task behavior, or anticipation for the onset of
reward in the onset type. Differences were noted in the feature of these responses between the
primary and higher-order cortices. It is indicated that the primary cortices represent the gustatory
nature of cues or reward, and the higher-order cortices the behavioral context of cues or reward.