Last year I reviewed a number of studies examining brain differences between children with autism and typically developing peers (see for example White matter differences in children with autism, Autism and the corpus callosum). Previous studies have usually compared children with autism to typically developing children. To some extent this group-differences approach assumes homogeneity of syndrome presentation, which may not reflect the continuum and diversity of autism spectrum disorders.
In a study to be Published in the Journal of Child Psychology and Psychiatry, Dr. C. Cheung and colleagues at the University of Hong Kong proposed that a “symptom-based” analysis of brain correlates in autism may better capture more subtle anomalies in the structural integrity of the brains of individuals with autism.
To this end, the authors examined MRI results of 14 children (age 6-14) with a ICD-10-based diagnosis of autism obtained via ADI-R but without any additional co-morbid condition. These children were compared to 14 matched typically developing kids. Specifically, the authors were interested in examining relations between ‘fractional anisotrophy’ and severity of symptoms. Fractional anisotrophy is a relatively new indicator of white matter integrity (instead of simply white matter volume).
1. When compared to typically developing peers, children with autism displayed significantly lower fractional anisotrophy in the prefrontal lobes, right ventral temporal lobe, left middle temporal lobe, and left cerebellar hemisphere. In addition, children with autism displayed higher fractional anisotrophy in the superior longitudinal fasciculus and the left occipital lobe.
2. ADI-A scores (anomalies in social interactions) were associated with lower fractional anisotrophy in the fronto-striatal-temporal regions and the posterior corpus callosum,
3. ADI-B scores (anomalies n communication) were associated with lower fractional anisotrophy in the fronto-striatal area and the posterior corpus callosum
4. ADI-D scores (repetitive or stereotyped behaviors) were associated with lower fractional anisotrophy in the basal ganglia, temporo-parietal lobe, splenium of the corpus callosum and cerebellum.
In summary, the group-differences approach suggested that children with autism had anomalies in regions that had been previously identified as atypical in autism (prefrontal and ventral temporal lobes). However, when the authors examined correlates of fractional anisotrophy and specific symptoms, they found a much more complex picture of brain functioning in autism. Specifically, key symptoms of autism were associated with anomalies in areas of the brain involved in understanding the mental state of others, facial recognition, eye gaze, and understanding emotional states and gestures.
You may have noted however, that children with autism had greater fractional anisotrophy in two areas (superior fasciculus and left occipital lobe). The authors argued that this finding may be due to increase use of brain regions involved in working memory and visual processing. Therefore, these findings may reflect brain correlates of advanced non-verbal strategies used by individuals with autism to process verbal information.
Finally, some of you are familiar with the studies showing increased white matter volume in individuals with autism. Pure white matter studies suggest that children with autism have larger white matter volume, which has been interpreted as the result of impaired cell pruning during development. However, the current study confirms that the examination of pure white matter volume may not be sensitive enough to identify specific anomalies associated with autism symptoms.
On a unrelated programming note: Tonight we will start a technical transition of our blogging software, which we hope to complete by Sunday. During this time we will be unable to write additional reviews and the website may be down for a few hours this Saturday and Sunday. We hope to continue our posts on Monday May 11th. Thank you for your patience!
Cheung, C., Chua, S., Cheung, V., Khong, P., Tai, K., Wong, T., Ho, T., & McAlonan, G. (2009). White matter fractional anisotrophy differences and correlates of diagnostic symptoms in autism Journal of Child Psychology and Psychiatry DOI: 10.1111/j.1469-7610.2009.02086.x
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