The Amygdala

Abstract

As with other regions of the limbic system, the amygdala has close ties with the hypothalamus, although it differs from other limbic structures in also having a close relationship to the basal ganglia. Thus the amygdala has a special place among the subcortical nuclear masses in being intimately involved in both limbic and striatal activities. This dual association suggests that there would be a corresponding division within amygdalar nuclei. As mentioned in the first chapter, there is a basic differentiation among the nuclei of the amygdala into corticomedial and basolateral groups, with the corticomedial group thought to be more closely linked to the basal ganglia (Crosby et al., 1962). In this connection, however, it is surprising that the lateral and basal nuclei of the amygdala are extremely rich in cholinesterase in the rat (Girgis, 1972). High acetycholine and cholinesterase activities have been associated with the basal ganglia to a greater extent than with the limbic system. On this basis, the corticomedial division might have been anticipated to be the one with the greatest cholinergic activity. However, as will be discussed later, it is doubtful that the diverse functions of the amygdala can be definitely related to any known anatomical groupings. In any case, as with other limbic structures, the amygdala is not homogeneous with regard to either structure or function.