Using MRI brain
scans, researchers found that the area of the brain called the
amygdala was, on average, 13 percent larger in young children with
autism, compared with control group of
children without autism. In the study, published in the latest
Archives of General Psychiatry, researchers scanned 50 toddlers
with autism and 33 children without autism at age 2 and again at
age 4. The study adjusted for age, sex and IQ.
"We believe that
children with autism have normal-sized brains at birth but at some
point, in the latter part of the first year of life, it [the
amygdala] begins to grow in kids with autism. And this study gives
us insight inside the underlying brain mechanism so we can design
more rational interventions," said lead study author Dr. Joseph
Piven.
A normal-sized
amygdala helps a person process faces and emotions, behavior
commonly known as joint attention.
"When you see a
face, you scan it, identify if it's friend or foe and make a
decision about whether to move forward or avoid it," said Dr. Barry
Kosofsky, chief of neurology at Cornell Medical Center, who was not
affiliated with the study.
UNC researchers
conducted diagnostic assessments, in addition to the MRI scans, to
monitor the children's behavior. They found toddlers with a large
amygdala also had joint attention problems. 
Watch Dr. Gupta explain the findings
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"We would basically
try to get the child to look one way, we'd turn and point to a
clock and see whether or not the child would notice it," explained
Piven. "The 2-year-olds without autism would see your face, see
where you are looking and join you but the children with autism,
with large amygdalas, would not."