[Neural mechanisms of intelligence, emotion, and intention]

Abstract

The limbic system (comprising the amygdala and the anterior cingulate cortex) and the prefrontal cortex (the orbital and dorsolateral prefrontal cortices) have been implicated in emotional and behavioral control. Selective lesion studies in rodents suggest that the basolateral nucleus of the amygdala, which is a critical subnucleus within the amygdala, plays a critical role in appetitive instrumental behaviors. On the other hand, the central nucleus of the amygdala directly receives afferents from the lateral nucleus of the amygdala. These 2 nuclei (central and lateral) of the amygdala are implicated in the learning of reflexive behavior (e.g., orienting, startle, and approaching behaviors) and autonomic responses (e.g., heart rate and blood pressure) during pavlovian conditioning. The caudal part of the anterior cingulate cortex (cognitive subdivision) is involved in monitoring and evaluating of the outcome of an indivisual's actions. However, the orbital cortex and the rostral part of the anterior cingulate cortex (affective subdivision) is involved in the biological evaluation of external sensory stimuli and events induced by stimuli originating from sources other than the individual. Based on these functions, the cognitive subdivision of the anterior cingulate cortex contributes to guiding and selecting actions that yield the optimal outcome, while the affective subdivision focuses on external aversive or rewarding stimuli, and guides appetitive or avoidance behaviors toward or away from these external stimuli. The dorsolateral prefrontal cortex is involved in predicting of the outcome of own action, and the evaluation of the outcome for guiding optimal behaviors is based on its close reciprocal connections with the limbic system. These 4 regions of the brain interact with each other and work complementarily. In the present review, the abovementioned functions of the limbic system and prefrontal cortex in primates are discussed with regard to the findings of previous neurophysiological studies in which neuronal responses in these brain regions were analyzed in monkeys and rats.