Most Autistic People Have Normal Brain Anatomy

A new paper threatens to turn the world of autism neuroscience upside down. Its title is Anatomical Abnormalities in Autism?, and it claims that, well, there arent very many.

Published in Cerebral Cortex by Israeli researchers Shlomi Haar and colleagues, the new research reports that there are virtually no differences in brain anatomy between people with autism and those without.

What makes Haar et al.s essentially negative claims so powerful is that their study had a huge sample size: they included structural MRI scans from 539 people diagnosed with high-functioning autism spectrum disorder (ASD) and 573 controls. This makes the paper an order of magnitude bigger than a typical structural MRI anatomy study in this field. The age range was 6 to 35.

The scans came from the public Autism Brain Imaging Data Exchange (ABIDE) database, a data sharing initiative which pools scans from 18 different neuroimaging centers. Haar et al. examined the neuroanatomy of the cases and controls using the popular FreeSurfer software package.

What did they find? Well not much. First off, the ASD group had no differences in overall brain size (intracranial volume). Nor were there any group differences in the volumes of most brain areas; the only significant finding here was an increased ventricle volume in the ASD group, but even this had a small effect size (d = 0.34). Enlarged ventricles is not specific to ASD by any means the same thing has been reported in schizophrenia, dementia, and many other brain disorders.

Heres some of the data: each double bunch of dots represents one of the research sites, with grey being the autistic brains and black the controls. Each row contains the data from one part of the brain. You can see that theres just not much difference. While a few sites find differences in a few measures, theyre not consistent across sites. Only ventricle volume (bottom row) is different overall.

A detailed cortical morphometry analysis of the brains did find a few statistically significant results in cortical thickness, but not other metrics:

Individuals with ASD exhibited significantly thicker cortex than controls in several areas including the right and left occipital poles, left middle occipital sulcus, left occipital-temporal sulcus [however] there were no significant differences in volumetric or surface area measures between groups. There were also no significant volumetric differences between groups in any of the subcortical areas.

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Most Autistic People Have Normal Brain Anatomy