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The amygdala is actually several separately functioning nuclei that have been grouped together by their anatomical proximity. Key among these nuclei are the basolateral complex, the central nucleus, and the medial amygdala. The basolateral complex receives input from the sensory systemSee also sense A sensory system is a part of the nervous system that consists of sensory receptors, neural pathways, and those parts of the brain responsible for processing the information. Specific sensory systems are those for somatic sensation, vision,s and is necessary for fear conditioningFear conditioning is a form of learning in which fear is associated with a particular neutral context (e. a room) or neutral stimulus (e. This can be done by pairing the neutral stimulus with a shock. Eventually, the neutral stimulus alone brings the anim. The central nucleus is the main output for the basolateral complex and is involved in emotional arousal. It sends outputs to the hypothalamusIn the anatomy of mammals, the hypothalamus is a region of the brain located below the thalamus, forming the major portion of the ventral region of the diencephalon and functioning to regulate certain metabolic processes and other autonomic activities. for activation of the sympathetic nervous systemThe sympathetic nervous system (SNS) is one half of the autonomic nervous system; the parasympathetic nervous system (PNS) is the other. The sympathetic nervous system activates what is often termed the "fight or flight response" of the body. Some evoluti, the reticular nucleus for increased reflexes, the trigeminal nerveThe trigeminal nerve is the fifth (V) cranial nerve, and carries sensory information from most of the face, as well as motor supply to the muscles of mastication (the muscles enabling chewing), tensor tympani (in the ear) and other muscles in the floor of and facial nerveThe facial nerve is seventh of twelve paired cranial nerves. It emerges from the brainstem between the pons and the medulla, and controls the muscles of facial expression, and taste to the anterior two-thirds of the tongue. Its main function is motor cont for facial expressionA facial expression results from one or more motions or positions of the muscles of the face. They are closely associated with our emotions. Charles Darwin noted in his book The Expression of the Emotions in Man and Animal :. the young and the old of wides of fear, and the ventral tegmental area, locus ceruleus, and laterodorsal tegmental nucleus for activation of dopamine, acetylcholine and epinephrine. The medial amygdala is involved in olfaction and pheremone processing. It receives input from the main and accessory olfactory bulb.

Fear conditioning, which trains animals to associate fear with other (previously neutral) stimuli, alters the information stored in the amygdala, as shown by experiments from Joseph Ledoux's lab and others. In this regard the amygdala serves as a simple Pavlovian learning machine that associates aversive events with neutral events, helping animals react to their world.

In language learning, some hypothesize that second language learning for adults may not make ready use of the amygdala in procedural memory usage and so emotional links to words are slower to form.