Brain scans of autistic children have revealed striking faults in key brain circuits that could explain the range of social difficulties such youngsters experience, neuroscientists claimed yesterday.
Detailed snapshots of the children's brains showed that networks of nerves thought crucial for understanding other people's emotions and intentions did not spark into life at the appropriate moment. The more severe a child's autism, the less activity the circuits showed.
In the study, neuroscientists led by Mirella Dapretto, a psychiatrist and brain mapping specialist at the University of California in Los Angeles, showed a series of faces to two groups of children with an average age of just over 12 years. The children in one group had been diagnosed with autism; the others showed no signs of the disorder.
Every child tested saw 80 faces, each of which expressed either anger, fear, happiness, sadness or a natural state. In separate scans, the children were asked to observe the face or imitate the expression.
The researchers found a striking difference between the brain scans of the two groups of surveyed children. When the non-autistic children saw the faces, various parts of their brains flickered into life, including clumps of nerves called mirror neurons. This group of nerves is thought to play a key role in helping us understand how others are feeling, for example by mirroring in ourselves feelings of sadness if we see someone looking miserable.
Significantly, brain scans showed that when autistic children looked at the faces, they processed the features properly, but the mirror neurons conveying the emotion of the expression failed to light up.
In the next test, children were asked to imitate the expression on each face flashed up before them. Again, the scans showed that clumps of mirror neurons burst into life in children with normally developed brains. When autistic children mimicked the expressions, they hardly flickered at all. The scans suggest that while people with autism can recognise expressions, the brain circuits that attach emotion to them are faulty, making it hard or impossible to read others' feelings.
The study, which was published in Nature Neuroscience yesterday, shows that the problem lies with a particular region of the brain known as the pars opercularis, which is rich in mirror neurons. In a final set of scans, the scientists showed that increasingly severe autism went hand in hand with rapidly decreasing activity of the mirror neurons.
"This mirroring mechanism may underlie the remarkable ability to read others' emotional states from a mere glance," said Dr Dapretto. "Our findings suggest that a dysfunctional mirror neuron system may underlie the social deficits observed in autism. This is exciting because we finally have an account that can explain all core symptoms of this disorder."
