The Human Amygdaloid Complex: Cellular Architecture and Dopaminergic Innervation

The human amygdaloid complex (AC) is associated with the perception of fear and consequent anxiety‐related behaviors, apart from other functions ranging from attention to memory and emotion. The AC is composed of several regions with specific cytoarchitectures, chemistry, and connections that encode different aspects of fear. Detailed understanding of AC cell composition is basic to determining whether cell number alterations coincide with neurological and psychiatric pathologies associated to anxiety imbalances, as well as with changes in brain functionality during aging. Here, we describe quantitative data gathered applying stereological methods to human AC tissue; the amounts of neurons, glial and endothelial cells, as well as of various interneuron subsets that populate the AC regions were noted and compared with those collected in the AC of non‐human primates and rodents. This chapter also addresses the dopaminergic innervation of the AC, which exerts a modulatory effect over the intrinsic AC network and is critical for reward‐related learning and fear conditioning. This innervation is twice as abundant in the main output nuclei as in the principal entry nuclei of the human AC, and this irregularity may indicate functional variations between these entry and output amygdaloid territories