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A number of fMRI studies of language processing in people who have autism and are high-functioning indicate some consistent differences in brain activation, compared to matched normal control subjects. Although the same or similar areas of the cortex become activated in autism as in controls, there are two indicators that the integration of information across cortical areas is lower in the group with autism. The first indicator is the lower level of synchronization in the brain activation among the activated areas in people with autism, particularly between anterior (prefrontal) areas and other areas. The second indicator is that the amount of activation in certain areas differs between the groups, such that generally, the group with autism tends to have less activation in areas that play an integrating role (or a role in figurative language processing) and have more activation in areas that tend to be involved in sensory and perceptual processing. For example, in sentence comprehension, the autism group shows reliably less activation than the control group in Broca's (left inferior frontal gyrus) area, and reliably more activation than the control group in Wernicke's (left laterosuperior temporal) area. Broca's area may be more involved in integration at the syntactic and thematic levels, whereas Wernicke's area may be more involved in lexical-level processing. These findings suggest that the neural basis of disordered language in autism entails a lower degree of information integration and synchronization across the large-scale cortical network for language processing. Similar conclusions from studies of problem-solving and other cognitive tasks converge on an underconnectivity account of autism, leading to difficulty in tasks requiring substantial inter-region integration in association areas. |
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