Role of the monkey amygdala in social cognition

Recent studies demonstrated the role of the primate amygdala (AM) in social cognition. In the present study, neuronal responses in the monkey amygdala were analyzed during discrimination of facial expressions and discrimination of various rewarding and aversive stimuli, such as food and objects associated with electric shock. The results indicated that activity of some amygdalar neurons preferentially increased in response to human facial expressions. Patterns of correlation coefficients between the different facial expressions indicated that facial expressions of a familiar person to the monkey were more discriminately represented than those of unfamiliar persons. Furthermore, responses of these neurons to facial expressions seemed to be independent of reward contingency. Other neurons responded to various objects that were biologically important, including food as reward and real humans. These amygdalar neurons displayed modulation of responses to the objects in various situations, including satiation and reversal, and modulation of responses to real humans who approached and withdrew from the monkey. These results suggest that there are at least two classes of amygdalar neurons: one type of neuron is involved in processes independent of one's own emotional state such as recognition of facial expression and inferring the emotional states of other persons, and the other type is involved in the ongoing evaluation of all sensory stimuli based on one's own emotional state. (C) 2003 Published by Elsevier B.V.