::Amygdala, The Biological Emotion Engine.

The existence of the amygdala was first formally recognized in the early 19th century. The name, derived from the Greek, was meant to denote the almond-like shape of this region in the medial temporal lobe. Much debate has since ensued, and continues today, about how the amygdala should be subdivided. Also controversial is how the subdivisions relate to other major regions of the brain.

One long-standing idea is that the amygdala consists of an evolutionarily primitive division associated with the olfactory system (cortical, medial and central nuclei) and an evolutionarily newer division associated with the neocortex (lateral, basal, and accessory basal nuclei). The areas of the older division are sometimes grouped as the cortico-medial region (cortical and medial nuclei) and sometimes as the centro-medial region (the central and medial nuclei). In contrast, the newer structures related to the neocortex are often referred to as the basolateral region. The almond shaped structure that originally defined the amygdala included the basolateral region rather than the whole structure now considered to be the amygdala.

In recent years, there have been a number of attempts to reclassify the amygdala and its relation to other areas. For example, Heimer and colleagues have argued for the concept of an extended amygdala. In this view, the central and medial amygdala form continuous structures with the lateral and medial divisions of the bed nucleus of the stria terminalis. A more radical notion comes from Swanson and Petrovich, who propose that idea that “the amygdala,” whether extended or not, does not exist as a structural unit. Instead, they argue that the amygdala consist of regions that belong to other regions or systems of the brain and that the designation “the amygdala” is not necessary. For example, in this scheme, the lateral and basal amygdala are viewed as nuclear extensions of the neocortex (rather than amygdala regions related to the neocortex), the central and medial amygdala are said to be ventral extensions of the striatum, and the cortical nucleus is associated with the olfactory system. While this scheme has some merit, the present review focuses on the organization and function of nuclei and subnuclei that, while traditionally said to be part of the amygdala, nevertheless perform their functions regardless of whether the amygdala itself exists, or whether it is extended.

The Function 

Although fear is the emotion best understood in terms of brain mechanisms, the amygdala has also been implicated in a variety of other emotional functions. A relatively large body of research has focused on the role of the amygdala in processing of rewards and the use of rewards to motivate and reinforce behavior. As with aversive conditioning, the lateral, basal, and central amygdala have been implicated in different aspects of reward learning and motivation, though the involvement of these nuclei differs somewhat from their role in fear. The amygdala has also been implicated in emotional states associated with aggressive, maternal, sexual, and ingestive (eating and drinking) behaviors. Less is known about the detailed circuitry involved in these emotional states than is known about fear.

Because the amygdala learns and stores information about emotional events, it is said to participate in emotional memory. Emotional memory is viewed as an implicit or unconscious form of memory and contrasts with explicit or declarative memory mediated by the hippocampus.

Basically its an amazing part of the brain, any damage to this can result in Cotards Syndrome and Capgras delusion as discovered by Dr. Vilayanur Ramachandran ( UCSD) and as mentioned in his papers.

Further Reading and Information Courtesy: My Brain(LOL), Dr. Vilayanur Ramachandran( UCSD).