The Amygdaloid Complex: Anatomy and Physiology

A converging body of literature over the last 50 years has implicated the amygdala in assigning emotional significance or value to sensory information. In particular, the amygdala has been shown to be an essential component of the circuitry underlying fear-related responses. Disorders in the processing of fear-related information are likely to be the underlying cause of some anxiety disorders in humans such as posttraumatic stress. The amygdaloid complex is a group of more than 10 nuclei that are located in the midtemporal lobe. These nuclei can be distinguished both on cytoarchitectonic and connectional grounds. Anatomical tract tracing studies have shown that these nuclei have extensive intranuclear and internuclear connections. The afferent and efferent connections of the amygdala have also been mapped in detail, showing that the amygdaloid complex has extensive connections with cortical and subcortical regions. Analysis of fear conditioning in rats has suggested that long-term synaptic plasticity of inputs to the amygdala underlies the acquisition and perhaps storage of the fear memory. In agreement with this proposal, synaptic plasticity has been demonstrated at synapses in the amygdala in both in vitro and in vivo studies. In this review, we examine the anatomical and physiological substrates proposed to underlie amygdala function.




FIG. 1. Nuclei of the rat amygdaloid complex. Coronal sections are drawn from rostral (A) to caudal (D). The different nuclei are divided into three groups as described in text. Areas in blue form part of the basolateral group, areas in yellow are the cortical group, and areas in green form the centromedial group. ABmc, accessory basal magnocellular subdivision; ABpc, accessory basal parvicellular subdivision; Bpc, basal nucleus magnocellular subdivision; e.c., external capsule; Ladl, lateral amygdala medial subdivision; Lam, lateral amygdala medial subdivision; Lavl, lateral amygdala ventrolateral subdivision; Mcd, medial amygdala dorsal subdivision; Mcv, medial amygdala ventral subdivision; Mr, medial amygdala rostral subdivision; Pir, piriform cortex; s.t., stria terminalis. See text for other definitions.




Sah, P., E. S. L. Faber, M. Lopez de Armentia, and J. Power.
The Amygdaloid Complex: Anatomy and Physiology.
Physiol Rev 83: 803–834, 2003; 10.1152/physrev.00002.2003.

http://physrev.physiology.org/cgi/content/full/83/3/803