Autism-class social disorder correlates with blood flow to the inferior frontal gyrus

The researchers studied "high functioning" autistic children, so they were isolating "pure" social disabilities from the cognitive disorders common in many forms of autism. In this group a functional MRI study provided one of the first objective tests for evaluating autism:

Science & Technology at Scientific American.com: Lack of "Mirror Neurons" May Help Explain Autism

... 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 nonautistic 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 activity in the pars opercularis of the inferior frontal gyrus--a brain region located near the temple.

This section of the brain has been shown by other studies to be part of the so-called mirror neuron system, which allows humans to understand the intentions of other human beings by observing their actions or imitating their behavior. When damaged, it can interfere with speech.

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.

These children could be said to suffer from 'isolated hypofunction of the inferior frontal gyrus' syndrome' (IHIFG Syndrome). If these results hold up we will be able to tease out some of the different conditions subsumed by the generic label of "autism".