Living without an Amygdala PDF
|Author||David G. Amaral and Ralph Adolphs|
|File size||22.69 MB|
|Category||Free Medical Books|
The amygdala, or more properly the amygdaloid complex, is about 2.0 cm3 on each side of the human brain. If a normal adult brain is approximately 1,300 cm3, then the amygdala makes up about 0.3% of its volume. The human amygdala has about 12 million neurons on each side. This compares to estimates of 100 billion neurons in the entire brain and 20 billion in the cerebral cortex. By any quantitative measure, the amygdala makes up a very small portion of the human brain. Yet there is virtually no psychiatric or neurological disorder in which it has not been suggested to play an important role. Why is the amygdala so popular in neuropsychiatry? And why edit a book on it?
The answer to these questions is that despite its small size, the amygdala is one of the most densely connected structures in the brain. This feature of connectivity, in turn, fits very well with hypotheses about not only psychiatric illnesses (that they are disconnection or misconnection syndromes in many cases), but also the functions that the amygdala is thought to implement. First and foremost among these latter hypotheses is that the amygdala helps orchestrate global organismic states that we call “emotions”—states that are pervasively dysfunctional in psychiatric illness, but that also show considerable variation across individual differences in the healthy population. In short, the reason for interest in the amygdala derives from its pervasive role: In implementing emotional states, it modulates nearly every cognitive function one can think of.
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