'Broken Mirror' May Cause Autism
When observing and imitating emotions, children with autism
display virtually no activity in a key part of the brain's
mirror neuron system, according to new imaging research
published in Nature Neuroscience.
The human brain has a matching system of observation and
execution that causes mirror neurons to fire both when a person
observes others performing a goal-directed action and when he or
she carries out the same action. This is the neural mechanism
that allows most people to automatically understand others'
actions, intentions and emotions, neuroscientists believe.
But autism is characterized by difficulties with social
interaction, including verbal and nonverbal communication,
imitation and empathy. The new findings dramatically bolster a
growing body of evidence pointing to a breakdown of the brain's
mirror neuron system as the mechanism behind these symptoms.
Dysfunctional Mirror Neuron System
"Our findings suggest that a dysfunctional mirror neuron system
may underlie the social deficits observed in autism," says
Mirella Dapretto, lead author and assistant professor in
residence of psychiatry and biobehavioral sciences at the Semel
Institute for Neuroscience and Human Behavior at UCLA and the
David Geffen School of Medicine at UCLA.
"Together with other recent data, our results provide strong
support for a mirror neuron theory of autism. This is exciting
because we finally have an account that can explain all core
symptoms of this disorder," Dapretto adds.
Researchers used functional magnetic resonance imaging (fMRI) to
measure brain activity in 10 high-functioning children with
autism while they imitated and observed 80 photos depicting
different emotions, such as anger, fear, happiness or sadness.
The brain activity of 10 typically developing children also was
studied while they performed the same tasks.
All of the children rehearsed the tasks prior to the fMRI scans
to assure researchers they could perform the tasks. Both groups
performed equally well. Normal brain activity in areas of the
brain involving sight and facial movements indicated that the
children with autism remained on task during the fMRI scans.
The team assessed symptom severity of each autistic child with
two independent measures: the Autism Diagnostic Observation
Schedule-Generic, and the Autism Diagnostic Interview.
Reduced Activity in the Emotion Centers
Unlike the typically developing children, the autistic children
showed virtually no activity in the part of the brain called the
pars opercularis of the inferior frontal gyrus, which has been
identified as a key part of the mirror neuron system in previous
research.
Importantly, the level of mirror neuron activity seen in
children with autism was inversely related to symptom severity
in the social domain.
Children with autism also showed reduced activity in the emotion
centers of the brain, consistent with the hypothesis that this
mirroring mechanism may play a crucial role for understanding
how others feel and for empathizing with them.
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