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Heightened Level Of Amygdala Activity May Cause Social Deficits In

Autism

ScienceDaily (Mar. 24, 2009) —

http://www.sciencedaily.com/releases/2009/03/090319132956.htm

Something strange is going on in the amygdala – an almond-shaped

structure deep in the human brain – among people with autism.

Researchers at the University of Washington have discovered an

increased pattern of brain activity in the amygdalas of adults with

autism that may be linked to the social deficits that typically are

associated with the disorder. Previous research at the UW and

elsewhere has shown that abnormal growth patterns in the amygdala are

commonly found among young children diagnosed with autism.

The amygdala is popularly associated with the " fight-or-flight

response " in dangerous situations. But it has other functions,

including identifying faces and situations and evaluating social

information such as emotions.

The new research shows that brain activation in adults with autism

remains elevated long after similar brain regions of typically

developed adults have stopped being activated when exposed to a series

of pictures of human faces. A decrease in activation over time to the

same type of information is called neural habituation and is connected

with learning, according to Natalia Kleinhans, lead author of the new

study and a UW research assistant professor of radiology.

" What we are seeing is hyperexcitability or overarousal of the

amygdala, which suggests that neurons in the amygdala are firing more

than expected, " said Kleinhans, who is associated with the UW Autism

Center.

" If you consider that habituation reflects learning in as simple a

task as looking at a face, slowness to habituate in people with autism

may contribute even more markedly to difficulty with more complex

social interactions and social cognition. If the brain is not reacting

typically to a static face with a neutral expression, you can imagine

how difficult it may be for someone with autism to pick up more subtle

social cues. "

The National Institute of Child Health and Human Development and the

National Institute of Mental Health funded the research, which appears

in the online edition of The American Journal of Psychiatry.

The UW researchers used functional magnetic resonance imaging to

examine brain activation in 19 individuals with autism and in a

comparison group of 20 healthy adults. The subjects ranged in age from

18 to 44 and the two groups were matched for IQs in the low-normal

range. Both groups had their brains scanned while they looked at

series of faces with neutral expressions. Each face appeared on a

screen for three seconds and occasionally a face would be repeated two

consecutive times. When that happened subjects were instructed to push

a button.

The scientists were interested in what happened in two brain regions,

the amygdala and the fusiform gyrus, when the subjects viewed the

faces. It turned out that the fusiform gyrus, which helps determine

what kind of object a person is looking at – a face or a house, for

example – showed no habituation in either group. But the differences

were striking when it came to the amygdala.

" The differences we found were in the amygdala and specific to the

amygdala, " said Kleinhans. " They originated there and did not go

across the brain. "

She said one theory about autism is that when this hyperarousal

occurs an individual misses important information. Those individuals

with autism who had the most social impairment exhibited the highest

levels of amygdala arousal.

" This is another piece of evidence that there is something wrong with

the amygdala in autism that contributes to social impairment. These

results help refine our understanding of functional abnormalities in

autism and are a new way of thinking about social dysfunction in

autism, " said Kleinhans.

Co-authors of the paper, who are all associated with the UW's Autism

Center, the radiology department or department of psychosocial and

community health, are L. , Todd s, Roderick

Mahurin, Greenson and Aylward. Geraldine Dawson,

founding director of the Autism Center who is now the chief scientific

officer of Autism Speaks, also contributed to the paper.

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