More than 1 in 500 children have some form of autism, according to the Centers for Disease Control.

Autism is a neurodevelopmental disorder that manifests itself in abnormal social interaction, communication ability, patterns of interests, and patterns of behavior. In general, people with autism suffer from a failure to develop normal speech, an absence of normal facial expression and body language, a lack of eye contact, a tendency to spend time alone, a lack of imaginative play, repetitive behavior, and obsession with particular objects or routines.

All autistic children suffer from an impaired ability to communicate and relate to others, but some of them are able to socially interact to a greater degree than their peers. A recent study which is to appear in the current issue of Nature Neuroscience, suggests there is a clear neurological cause for their social impairment.

Neuroscientist Mirella Dapretto of the University of California Los Angeles and her colleagues surveyed the brains of 10 autistic children and an equal number of non-autistic children as they watched and imitated 80 different faces displaying either anger, fear, happiness, sadness or no emotion. By measuring the amount of blood flowing to certain regions of the children's brains with a magnetic resonance imaging (MRI) machine, the researchers could determine what parts of the brain were being used as the subjects completed the tasks. The autistic children differed from their peers in only one respect: each showed reduced brain activity in a region known as the mirror neuron system.

The neurons in this area are active when the individual performs certain tasks, but they also fire when he/she watches someone else performing the same specific task. Thus, the neuron "mirrors" the behavior of somebody else, as though the observer were performing the action. These neurons have been observed in primates, some birds, and humans in Broca's and the inferior parietal cortex of the brain. Some scientists consider mirror neurons one of the most important findings of neuroscience in the last decade.
Although the high-functioning autistic children were able to imitate the facial expressions, they had trouble understanding the corresponding emotional state. The study suggests that the incompletely activated mirror neuron system is to blame. In fact, the less blood that flowed to this region of the brain in each autistic child, the less social ability that child showed -- providing more support for the apparent link.
Why is this region so important? It isn't really known. However, certain speculations have been made. In humans, mirror neurons are found in the inferior frontal cortex, close to Broca's area, which is a language region. Thus, the lack o social abilities may be linked to a deficiency in learning and using the language in general.

The presence of the mirror neurons in this area has also lead to suggestions that human language evolved from a gesture performance / understanding system implemented in mirror neurons. Mirror neurons certainly have the potential to provide a mechanism for action understanding, imitation learning, and the simulation of other people's behavior. However, like many theories of language evolution, there is little direct evidence either way.


Illustration by James Collins