The Role of the Amygdaloid Nucleus in Animal Behaviour

Abstract

This chapter discusses the role of the amygdaloid nucleus in animal behavior. The amygdaloid complex, which plays an integratory and regulatory role in important functions of the organism, such as food intake, defense, and sexual behavior, can be divided into two parts with different or even opposite physiological meanings. The dorsomedial division is involved in defensive mechanisms. Its stimulation, producing various symptoms of fear and defense may serve as negative reinforcement (punishment) for the training of defensive conditioned reflexes both classical and avoidance. The basolateral part plays an inhibitory role. Its stimulation inhibits performance of the instrumental alimentary reactions, as well as food intake, and its destruction produces hyperphagia and disinhibition of conditioned alimentary reactions. This suggests that it plays the role of an alimentary inhibitory center duplicating the one in the ventromedial hypothalamus. However, stimulation of the basolateral part also inhibits fear symptoms and instrumental intertrial reactions connected with the generalized fear state. Stimulation of the dorsomedial part has properties of negative reinforcement. There is also a great deal of evidence suggesting that stimulation of the basolateral part is positively reinforcing. It is possible that the pleasant emotional state produced by basolateral stimulation may interfere with both feeding and defensive behavior and this may account for lack of the respective reactions.