A tiny part of the brain no bigger than a nut may carry the skills for reading emotions on other people's faces and could give a clue about the causes of autism, American doctors reported this week.

They reported in the science journal Nature that tests on a woman with a rare type of brain damage showed the amygdala, an almond-shaped area of the temporal lobe in the center of the brain, showed it has some very specific functions.The woman was less able to recognize expressions of anger and surprise on human faces than others tested, although she could still recognize the faces as different from one another.

"From our results, the amygdala appears necessary both to recognize the basic emotion of fear in facial expressions, and to recognize many of the blends of multiple emotions that the human face can signal," Antonio Damasio and colleagues at the University of Iowa wrote.

John Allman of the California Institute of Technology wrote in a commentary that the findings added support to theories that the amygdala has a central role in social communication.

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The results could give clues about the cause of autism, for example, which can cause children to disregard much normal human social behavior and to become completely uncommunicative.

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