A Description of Intra-amygdaloid Connections in Old World Monkeys

The intrinsic amygdaloid connections of the cynomolgus monkey were investigated using the autoradiographic method. Additional evidence concerning the origin of some intra-amygdaloid connections was provided by a series of rhesus monkeys with injections of horseradish peroxidase (HRP) in the amygdaloid complex. The experiments indicated that each of the major amygdaloid nuclei possesses a unique, organized set of intrinsic projections. Furthermore, there were large differences in the magnitude of the internal connections arising from or terminating in the various nuclei. The heaviest intrinsic projections arose from the lateral and basal nuclei while the central, medial, cortical, and accessory basal nuclei received the greatest number of these afferents. Thus, there was a clear trend for the bulk of these connections to run dorsally and medially within the amygdala. One important function of these intrinsic connections may be the integration of afferent sensory information from the various association areas which project to the amygdala.