The neurobiological mechanisms underlying autism remain largely unknown. Although preventing or curing autism is the ultimate goal, such a possibility does not appear to be within our grasp at this time. Thus, optimizing cognitive functioning may be a more pragmatic, but important, goal. In order to design optimal cognitive rehabilitation treatments, the organization of neural networks as well as the dynamic changes in the structure of these neural networks with cognitive development and remediation needs to be better understood. Because language is such an important aspect of human development, much interest is focused on remediating the language deficits found in autism.
Neuroimaging has provided some insight into the organization of the cognitive language processing network in individuals with autism. Functional magnetic resonance imaging and magnetoencephalography studies suggest that the brain may not process language in the same way in typically developing individuals and individuals with autism. During language tasks, functional magnetic resonance imaging activation is abnormally decreased or increased in typical language areas and increased in atypical cortical areas, in individuals with autism as compared to typically developing individuals.1–5
Magnetoencephalography has advantages over functional magnetic resonance imaging. Because it directly measures the magnetic fields emitted by active synapses, instead of the indirect blood-oxygen signal measured with functional magnetic resonance imaging, it allows the millisecond-by-millisecond temporal evolution of cortical activation pattern to be studied. This may be important since the timing of cortical activation is different in individuals with developmental cognitive disorders as compared to typically developing individuals. Second, the morphology and neurophysiological characteristics of the evoked magnetic field can be examined.
Previous magnetoencephalography studies have shown that the auditory evoked field follows an opposite pattern of hemispheric dominance maturation in individuals with autism as compared to typically developing individuals. While both typically developing individuals and individuals with autism demonstrated reduced lateralization to syllable stimuli in childhood, as age increases cortical activation has been shown to become left lateralized in typically developing individuals and right lateralized in individuals with autism.6
This suggests that individuals with autism eventually overuse the right hemisphere to process language, but that this language dominance does not develop until adolescents. Interestingly, evoked potential studies demonstrate similar findings for older children with Asperger Syndrome.7
None of the magnetoencephalography studies that have examined individuals with autism have used functional mapping to examine the spatiotemporal dynamics of cortical activation during language tasks. We provide two examples of the spatiotemporal dynamics of cortical activation during simple auditory receptive language tasks in an older child and an adolescent with high-functioning autism. Our results suggest that children with autism may demonstrate patterns of cortical reorganization similar to those indentified in developmental dyslexia,8,9
and cortical hyperexcitability, not unlike the neurophysiological characteristics described in Rett syndrome.10