A01Perception and prediction Neural bases of congruency-sequence effects on conflict costs
The higher animals, which lives in complicated environments, flexibly select the optimal actions, by applying various behavioral rules in adaptation to the current environment. As they have a wide repertoire of rules, the explicit stimuli in the current environment do not necessarily specify the optimal rule to apply. A rule has to be selected sometimes by trial and error, and multiple rules may indicate the same action in other cases. Therefore, the way to reinforce the applied rule with the obtained outcome should depend on the context, or state, in which the rule was applied. We have trained macaque monkeys with a rule-switching task, in which the target-selection rule switches between matching with the sample in color and matching with the sample in shape, and examined the effects of lesioning various parts of the prefrontal cortex on the task performance. We found that monkeys select the target by applying one of the two rules by trial and error in trials following an error, and that the quick learning of the correct rule after a success under the trial and error mode is abolished by lesioning the orbital part of the prefrontal cortex (orbitofrontal cortex). In the trial and error mode, the subject has to exactly remember the rule that it applied in the immediately past target-selection and update the value of the rule according to the outcome. We have hypothesized that the orbitofrontal cortex represents the internal cognitive state in which an action is selected and thereby controls the learning when the outcome is provided. In the present project, we add the trial conditions in which one of the two rules does not specify the target (neutral conditions) to the rule-switching paradigm so as to increase the analysis power. We change experimental subjects from monkeys to humans, and examine the hypothesis that the orbitofrontal cortex represents the internal cognitive state by using psychophysics and functional magnetic imaging of brain activity. As the orbitofrontal cortex is subject to signal loss due to susceptibility artifacts, we also make efforts to optimize the imaging method to the orbitofrontal cortex.