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From JAMA |

Organization in Autism

Rajesh Kana, PhD; Alan Percy, MD
Arch Neurol. 2012;69(7):906-907. doi:10.1001/archneurol.2011.3596.
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The preliminary report by Courchesne and colleagues1 on the postmortem study of prefrontal brain tissue published in the November 2011 issue of JAMA is a novel and innovative account of brain organization in autism spectrum disorders. Their study addresses increased neuronal count in the prefrontal cortex against the backdrop of one of the relatively more consistent morphometric findings in autism, larger brain volume. Neuroimaging findings in the last 8 years or so have by and large been pointing to the prefrontal cortex as the epicenter of brain abnormalities in autism, with several reports of functional, anatomical, and connectional defects. In their previous work, Courchesne and colleagues2 examined the frontal cortex volume using neuroimaging and found enlarged gray matter and white matter volumes in individuals with autism. With the new findings of the increased number of neurons in a sample of young children and adolescents, one important question raised is how that impacts the functional and anatomical connections in the brains of people with autism. In addition to overconnectivity within the frontal cortex,3 long-distance functional underconnectivity between frontal and parietal lobes has also been reported in people with autism.46 It would be interesting and highly informative to examine how an increase in neuron number could contribute to altered patterns of functional and anatomical connectivity. One possible line of evidence in this direction pertains to the abnormally small and numerous minicolumns found in the frontal cortex of people with autism.7,8 Smaller and numerous minicolumns may lead to increased local connectivity, which in turn may lead to a hyperspecific brain. In other words, an increased neuronal count in the frontal lobe may result in altered patterns of connectivity. Another related thought is how an increase in the number of neurons contributes to white matter organization and connectivity. This is especially valid considering previous findings of increased white matter volume in the frontal lobe2,9 and the recent diffusion tensor imaging findings of reduced white matter integrity in the frontal lobe in autism.10,11 While Courchesne and colleagues1 have focused on the frontal lobe in this study, it would be worthwhile to examine the neuron count in other lobes too, especially the temporal and parietal lobes. In the Carper et al study,2 in addition to the frontal lobe, the authors also found a significant increase in gray matter in the temporal lobe and an increase in white matter in the parietal lobe in autism. Considering this finding as well as other functional connectivity studies pointing to frontal-parietal underconnectivity and a possible parietal autonomy in autism, examining other lobes will provide a comprehensive account of the brain organization in autism.


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