The amygdala is an almond-shaped collection of gray matter nuclei located in the anteromedial temporal lobe. It is a complex structure composed of multiple anatomically distinct nuclei rather than a single homogeneous mass.

The amygdala forms part of the limbic region of the telencephalon and occupies the anterior end of the temporal lobe, immediately anterior to the hippocampal formation.

Location

General Position

The amygdala is located:

In the anterior temporal lobe
Deep to the uncus
Anterior to the hippocampus
Inferomedial to the globus pallidus
Adjacent to the temporal horn of the lateral ventricle

Gross Morphology

Feature	Description
Shape	Almond-shaped
Color	Gray matter
Length	Approximately 15-20 mm
Width	Approximately 10-15 mm
Hemisphere	Present bilaterally
Region	Medial temporal lobe

In coronal sections, the amygdala appears as a rounded mass of gray matter occupying the anterior portion of the temporal lobe.

Major Nuclear Groups

Histologically and functionally, the nuclei of the amygdala divide into three primary groups, flanked by specialized GABAergic clusters.

Nuclear Group	Constituent Nuclei	Cytology & Primary Afferents	Main Efferents / Role
Basolateral Complex (BLA)	• Lateral nucleus (LA) • Basal nucleus (BA) • Accessory basal (AB)	Cortical-like pyramidal projection neurons; glutamatergic. Receives sensory thalamus, sensory neocortex, and hippocampus.	Primary sensory receptive zone; encodes stimulus salience and associative conditioning. Projects to CeA and ventral striatum.
Centromedial Group	• Central nucleus (CeA) • Medial nucleus (MeA)	Striatal-like medium spiny neurons; primarily GABAergic. Receives inputs from BLA, brainstem autonomic nuclei, and visceral afferents.	Chief autonomic/behavioral motor output hub. Projects to hypothalamus and periaqueductal gray (PAG).
Cortical / Superficial Group	• Anterior amygdaloid area (AAA) • Nucleus of the lateral olfactory tract • Cortical nuclei	Olfactory-related cortex-like layers. Receives direct, unthalamized inputs from the olfactory bulb.	Pheromonal, reproductive, and chemosensory valence routing.
Intercalated Cell Masses (ITC)	Dense paracapsular clusters of GABAergic interneurons	Interspersed between the BLA and CeA fiber tracts.	Acts as an inhibitory gate; critical substrate for fear extinction and prefrontal regulation.

Principal Cell Types

Cell Type	Characteristics
Projection neurons	Large excitatory neurons
Interneurons	Small inhibitory neurons

Common Interneuron Classes

Parvalbumin-positive neurons
Somatostatin-positive neurons
Calbindin-positive neurons

Blood Supply

The major arteries of the brain and the brain stem (inferior view).

Artery	Contribution
Anterior choroidal artery	Major supply
Anterior temporal branches	Supplemental supply
Posterior cerebral artery branches	Supplemental supply

Venous Drainage

Vein
Deep middle cerebral vein
Basal vein
Temporal venous tributaries

Development

The amygdala develops from both pallial and subpallial embryonic territories.

Embryological Region	Adult Nuclei
Pallial amygdala	Lateral, Basal, Accessory Basal nuclei
Subpallial amygdala	Central and Medial nuclei

This dual developmental origin contributes to the anatomical diversity of its nuclei.

Amygdala: Anatomy