Amygdala Shrinks in Autism, December 5, 2006

U.S. scientists have found the brain's "fear center" likely shrinks in autism's most severely socially impaired males with autism spectrum disorders.

The federally funded University of Wisconsin study showed teenagers and young men who were slowest at distinguishing emotional from neutral expressions and gazed at eyes least -- indicators of social impairment -- had a smaller-than-normal amygdala, an almond-shaped danger-detector deep in the brain.

The researchers also linked such amygdala shrinkage to impaired nonverbal social behavior in early childhood.

The researchers say their findings suggest social fear in autism may initially trigger a hyperactive, abnormally enlarged amygdala, which eventually gives way to a toxic adaptation that kills amygdala cells and shrinks the structure.

Richard Davidson and colleagues report on their magnetic resonance imaging study in the December issue of the journal Archives of General Psychiatry.