Categorical representation of objects in the central nucleus of the monkey amygdala

The primate amygdala consists of several subnuclei. Neurons in this brain area have been known to respond to stimuli belonging to specific categories of objects, such as faces, animals, and artifacts. However, little is known about the functional differences among the nuclei of the primate amygdala. To clarify functional differences among these subnuclei in object categorization, we compared the responsiveness of neuronal populations among the lateral, basal and central nuclei of the monkey amygdala. The activity of 203 neurons was recorded while video clips of 13 stimuli belonging to three categories (monkey, human, and artifact) were presented. Of these neurons, 37, 39 and 37 neurons in the lateral, basal and central nuclei, respectively, responded to at least one of the stimuli. We applied a cluster analysis to the neuronal population responses from these nuclei, and also calculated information about the three categories and monkey identity from each neuronal population. We found that the three categories and monkey identity could be more properly classified by neuronal responsiveness in the central nucleus, which is an output gate of the amygdala, than by that in the lateral and basal nuclei. These results suggest that the information about objects suitable for the generation of appropriate emotional response is built up within the primate amygdala via an intra-amygdala network from the lateral nucleus to the central nucleus.