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 brains 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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