"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 aren’t 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.
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.
I think this is an important paper and one that the autism field will need to take very seriously. There are hundreds of studies claiming to have found differences in brain structure in autism, many with small sample sizes, and Haar et al’s failure to replicate almost any of these claims, is sobering. It’s important to remember, however, that this paper only considered brain anatomy. It doesn’t contradict studies looking at brain function, nor does it relate to microanatomy or neuropathology (i.e. microscope work.)
As far as it goes, though, it’s a bit of an earthquake – and I’m not sure how much of the field is left standing."