Previous studies have demonstrated a lower degree of synchronization among activated brain areas in people with autism, as well as smaller size of the corpus callosum, the white matter that acts as cables to wire the parts of the brain together. This latest research shows for the first time that the abnormality in synchronization is related to the abnormality in the cabling. The results suggest that the connectivity among brain areas is among the central problems in autism. The researchers have also found that people with autism rely heavily on the parts of the brain that deal with imagery, even when completing tasks that would not normally call for visualization.
"Human thought is a network property. You think not with one brain area at a time, but with a network of collaborating brain areas, with emphasis on collaborating. In autism, the network connectivity (the bandwidth) through which the areas communicate with each other may be limited, particularly in the connections to the frontal cortex, limiting what types of networks can be used," said Marcel Just, co-author of the studies and director of Carnegie Mellon's Center for Cognitive Brain Imaging.
Both studies focused on people with autism who have normal IQs. In one study, the researchers used functional magnetic resonance imaging (fMRI) to view which parts of the brain were activated in people with autism compared to a control group of normal participants while completing the Tower of London task. In a Tower of London task, participants must -- in a set number of moves -- rearrange the positions of three distinctive balls in three suspended pool pockets to match a specified pattern. This requires a person to strate gize and plan several moves ahead.
The experiment confirmed the authors' previous findings that people with autism suffer from a lack of synchronization among brain regions, which helps to explain why some people with autism have normal or even superior skills in some areas, while many other types of thinking are disordered. In addition, their findings particularly implicate the lower synchronization between the frontal cortex and other portions of the brain. They have discovered that key portions of the corpus callosum seem to play a role in the limitation on synchronization. In people with autism, anatomical connectivity -- based on the size of the white matter -- was found to be positively correlated with functional connectivity, which is the synchronization of the active brain regions. They also found that the functional connectivity was lower in those participants in whom the autism was more severe. The study will be published in the journal Cerebral Cortex.
The second study, to be published in the journal Brain, examined a long-standing belief, supported through scientific research as well as anecdotal accounts, that people with autism rely heavily on visualization to process information. Temple Grandin, a professor at Colorado State University who has autism, says in her autobiography "Thinking in Pictures" that "Words are like a second language to me. ?When someone speaks to me, his words are instantly translated into pictures."
To test this relationship between the language and visuospatial systems of the brain, the team used fMRI scans to view the patterns of activation in the brains of autistic and normal participants while they read a series of sentences to determine whether each one was true or false. The sentences either had high imagery content ("The number eight when rotated 90 degrees looks like a pair of eyeglasses") or low imagery content ("Addition, subtraction and multiplication are all math skills.")
The fi ndings confirmed that the regions of the brain associated with visualization were activated when participants with autism read both kinds of sentences, while those regions of the brain were only activated when the control group read the high-imagery sentences. The results also replicated the researchers' findings in the Cerebral Cortex study, in that functional connectivity was lower among participants with autism, and that structural connectivity was positively correlated with functional connectivity. The authors believe that the heavy reliance on visualization by people with autism may be an adaptation to compensate for their lower ability to call on frontal regions of the brain.
"Thinking in autism is an adaption to the brain that Mother Nature provided. We now have evidence of a systematic relation between the properties of the brain and the properties of the thinking in autism," said Just, the D.O. Hebb Professor of Psychology at Carnegie Mellon.