ScienceWeek

Current Biology, Vol 17, R868-R874, 23 October 2007

http://scienceweek.com/2007/071028g.htm

Neuroscience: On the Amygdala

Joseph LeDoux

The amygdala is a complex structure involved in a wide range of normal behavioral functions and psychiatric conditions. Not so long ago it was an obscure region of the brain that attracted relatively little scientific interest. Today it is one of the most heavily studied brain areas, and practically a household word. Art critics are explaining the impact of a painting by its direct impact on the amygdala; essential oils are said to alter mood by affecting the amygdala; and there is a website where you can unleash your creativity by clicking your amygdala, and thereby popping your frontal cortex. In this Primer, I will focus on the scientific implications of the research, discussing the anatomical structure, connectivity, cellular properties and behavioral functions of the amygdala.

The amygdala was first recognized as a distinct brain region in the early 19th century. The name, derived from the Greek, was meant to denote an almond-like shape structure in the medial temporal lobe. Like most brain regions, the amygdala is not a single mass but is composed of distinct subareas or nuclei. The almond shaped area that gives the amygdala its name was really only one of these nuclei, the basal nucleus, rather than the whole structure.

Nuclei within brain areas like the amygdala are typically distinguished on the basis of histological criteria such as the density, configuration, shape and size of stained cells, the trajectory of fibers, and/or chemical signatures. Recently, more subtle measures, such as microscopic features of processes (axons and dendrites) have also been used. There has been much debate about how the amygdala should be partitioned on the basis of the various criteria, and how the subdivisions relate to other brain regions.

One long-standing idea is the amygdala consists of an evolutionarily primitive division associated with the olfactory system (the cortico-medial region) and an evolutionarily newer division associated with the neocortex (the basolateral region). The cortico-medial region includes the cortical, medial, and central nuclei, while the basolateral region consists of the lateral, basal and accessory basal nuclei. More recently, however, it has been argued that the amygdala is neither a structural nor a functional unit, and instead consists of regions that belong to other regions or systems of the brain...

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limbic system
amygdala
neuroscience
biopsychology