Many children and adults with autism lack, to a greater or lesser degree, the innate ability to grasp and interpret the meanings of gestures, body movements, tone of voice, and facial expressions. Now researchers are using brain-imaging technologies to discover why the brains of children with autism fail to process social inputs.

One powerful tool for such research is functional magnetic resonance imaging, or fMRI. The MRI scanner uses a large magnet to deliver magnetic pulses that induce a tiny radio signal in the part of the body being scanned. Computers detect the signals and generate images from them.

With fMRI, fast scanning techniques allow investigators to trace the flow of blood in the brain, which increases in areas where the brain is working harder. By comparing images when the brain is “at work” or “at rest,” investigators can see which regions become more active during mental tasks.

Scientists are using fMRI to study the brain’s mirror neuron system in children with autism. Mirror neurons fire when a person performs an action with a goal in mind or watches someone else perform an action. Neuroscientists think that mirror neurons allow one person to understand the actions, intentions and emotions of another.

Mirella Dapretto, an associate professor of psychiatry and biobehavioral sciences at UCLA, and her team have used fMRI to study the activity of mirror neurons in the brains of 10 children with autism. She also studied 10 normally developing children. First she used behavioral measures to assess the children’s ability to imitate and empathize with others. Then she captured fMRI images of brain activity as the children viewed and imitated pictures of faces depicting anger, fear, happiness or sadness.

Those children who best imitated social behaviors or best empathized with others had more brain activity in the brain’s right inferior frontal gyrus. Those who showed the greatest deficits in imitation and empathy had less activity in that region, which is known to be an important area of mirror neuron activity.