Decreased Interhemispheric Functional Connectivity in Autism
Abstract
The cortical underconnectivity theory asserts that reduced long-range functional connectivity might contribute to a neural mechanism for autism. We examined resting-state blood oxygen level–dependent interhemispheric correlation in 53 males with high-functioning autism and 39 typically developing males from late childhood through early adulthood. By constructing spatial maps of correlation between homologous voxels in each hemisphere, we found significantly reduced interhemispheric correlation specific to regions with functional relevance to autism: sensorimotor cortex, anterior insula, fusiform gyrus, superior temporal gyrus, and superior parietal lobule. Observed interhemispheric connectivity differences were better explained by diagnosis of autism than by potentially confounding neuropsychological metrics of language, IQ, or handedness. Although both corpus callosal volume and gray matter interhemispheric connectivity were significantly reduced in autism, no direct relationship was observed between them, suggesting that structural and functional metrics measure different aspects of interhemispheric connectivity. In the control but not the autism sample, there was decreasing interhemispheric correlation with subject age. Greater differences in interhemispheric correlation were seen for more lateral regions in the brain. These findings suggest that long-range connectivity abnormalities in autism are spatially heterogeneous and that transcallosal connectivity is decreased most in regions with functions associated with behavioral abnormalities in autism. Autism subjects continue to show developmental differences in interhemispheric connectivity into early adulthood.
The authors acknowledged that limiting their study to high-functioning young autistic males restricted their findings from being extended to females, younger children or lower-function ASD patients. Nevertheless, Anderson and colleagues emphasized that “Our finding adds to growing evidence that abnormalities of interhemispheric connectivity in autism are widespread but regionally specific and related to cognitive and neurological impairments commonly found in the disorder.”
The authors posited that their findings highlight MRI as a potential tool to assist physicians in diagnosing and treating autism.
The authors posited that their findings highlight MRI as a potential tool to assist physicians in diagnosing and treating autism.
In one breath the study authors acknowledge that the exclusion of low functioning autistic patients restricted their findings from being extended to those patients (or to other excluded groups, including females and younger children). In the next breath though, and in the title of their report and magazine articles the study findings are reported as being applicable to autism generally.
"However, research in ASD has tended to use overwhelmingly White, middle to upper middle class samples, and has often excluded children with multiple disabilities and/or severe to profound intellectual disabilities".
The lip service qualifying statement in this recent fMRI study report did not preclude the authors from making generalizations about autism as found across the spectrum notwithstanding the exclusion of low functioning autistic persons from the study. Articles commenting on this and other studies may or may not repeat that qualification. Most certainly all will be accompanied by headlines reporting new "autism" findings. Low functioning autistics are routinely excluded from major media institutions that like to focus on the barely affected, very high functioning persons with Aspergers or HFA, the Ari Ne'emans, Alex Planks, JohnMichelle Dawsons and Temple Grandins.
As in the popular media, so too in "scholarly", "scientific" research. "Autism" just doesn't meant what it use to.
Alleged "autism" spectrum research is anything but representative of the autism "spectrum" disorders.
i don't think the autistics in those studies have the functioning level of michelle dawson, ari ne'eman et. al.
ReplyDeleteIf it were feasible to include low functioning autistics, who have compliance issues in fMRI studies, I am sure there are a lot of researchers who would be happy to do so. If you had any suggestions as to how LFAs could be imaged in fMRI studies so that there were not problems with them moving around and producing artifacts, compliance to tasks, etc., I am sure a lot of scientists would welcome your suggestions with open arms.
Thank you Jonathan but I disagree with your assumptions about the inability to have low functioning autistic subjects in fMRI studies. My son's diagnosis is Autistic Disorder and he is assessed with profound developmental delays. As challenging as his behavior can be at times there are ways to manage the behavior. ABA has been very helpful for us in that area. I have just recently taken Conor to the dentist for a check up which included x-rays taken at a standing x-ray machine which required him to bite on uncomfortable wedges inserted into his mouth. He did very,very well. When I required similar procedures even more recently I was extremely uncomfortable and realized just how well Conor had done.
ReplyDeleteI would like to see study authors state that they could not use low functioning autistic subjects for the reasons you assume. Until then I don't accept that view. No offense.
The other concern I have is that since these studies are in fact using only HFA their reports, including titles, and any media coverage should make it clear that they do not necessarily apply to LFA persons.
Thanks for your comments, they are courteous and on point, as always.