Abstract | Summary | Original Article

Cortical activation and synchronization during sentence comprehension in high-functioning autism: Evidence of underconnectivity

Just MA, Cherkassky VL, Keller TA, Minshew NJ

Brain 2004; 127(8): 1811-1821

Question: Can the functional magnetic resonance imaging (fMRI) results from this study showing brain variations help explain some of the learning and perceptual differences in people with high functioning autism?

Background: Over the past several years, more and more studies have demonstrated that the brains of children with autism spectrum disorders (ASDs) differ from those of typically developing children. The usual finding is that the brain is larger, with increases in both white matter (the fibres that provide connections between brain cells) and grey matter (the brain cells that are involved in processing).

At the same time, there has been research that looked at the abnormal psychological (mental processing) features that are specific to people with ASDs. One of these, weak central coherence, refers to the inability to ?see the forest for the trees.? People with autism seem to focus on minor details while being unable to perceive or understand the larger picture. This dysfunction is partly explained by the inability to hold a single piece of information in the mind while relating it to another.

The authors of the current study relate their findings from functional MRI studies of people with high functioning autism to the psychological deficits (such as weak central coherence) and talents seen in people with autism.

Participants: The participants were 17 persons with a diagnosis of high functioning autism (that is, both verbal and full scale IQ above 80). The 17 control participants were community volunteers. The participants with autism were matched to their controls on the basis of age, IQ, gender, race and their family’s socioeconomic status. All were screened for genetic and medical disorders, as well as for psychiatric or neurological disorders.

Method(s): The participants were asked to read a sentence and then respond to questions about it. Functional magnetic resonance imaging (fMRI) was done to see which portions of the brain were activated during the performance of the tasks.

Main Results: There were significant differences between the two groups in the activation of language areas in the brain. Broca’s area and Wernicke’s area, portions of the brain that are associated with language functions, “lit up” on the fMRI scans in different ways. Wernicke’s area is important to the ability to identify individual words, while Broca’s area acts to integrate a number of functions associated with language comprehension and use. In the people with autism, there was greater activation of Wernicke’s area and less activation of Broca’s area than in the control group. In the participants with autism, there was a reduction in the speed and intensity of communication between the two areas, that is, the activation of the two areas should have been synchronized, but was not in the participants with autism.

Conclusions: There were significant differences between the fMRI findings in the group with high functioning autism and the typically developing group. The two language areas activated at different rates in the participants with autism, rather than lighting up simultaneously during a task, as in the typical controls. This finding may help to explain why people with autism seem to get stuck on single words, (i.e., single details), rather than being able to comprehend the meaning of a sentence. It is possible that the signal diminishes when traveling from Wernicke’s area, the brain site in which there is an initial recognition of words and subsequently meaning attached to them, before it reaches Broca’s area, in which it can be transformed into spoken or written language. It is possible that the “underconnectivity” is related to the excessive white matter accumulation in the brains of people with autism, which, rather than doing its job of creating connections between processing parts of the brain, actually interferes with the connections because it inhibits transmission of the signals from one area to another.

Further studies are necessary, but the authors present an entirely plausible picture of why people with autism have the deficits they have, and the “islands of genius” that some have. The findings offer an explanation, too, for hyperlexia, a condition in which people are able to read complex text without understandings its meaning. Taking part in social relationships requires that connections be made between brain areas responsible for the recognition of facial expressions, tone of voice, and expressions of emotion. It may be that these connections are slowed or even lacking in people with autism.