Neuroanatomical differences in brain areas implicated in perceptual and other core features of autism revealed by cortical thickness analysis and voxel-based morphometry

Abstract

Autism spectrum disorder is a complex neurodevelopmental variant thought to affect 1 in 166 [Fombonne (2003): J Autism Dev Disord 33:365-382]. Individuals with autism demonstrate atypical social interaction, communication, and repetitive behaviors, but can also present enhanced abilities, particularly in auditory and visual perception and nonverbal reasoning. Structural brain differences have been reported in autism, in terms of increased total brain volume (particularly in young children with autism), and regional gray/white matter differences in both adults and children with autism, but the reports are inconsistent [Amaral et al. (2008): Trends Neurosci 31:137-145]. These inconsistencies may be due to differences in diagnostic/inclusion criteria, and age and Intelligence Quotient of participants. Here, for the first time, we used two complementary magnetic resonance imaging techniques, cortical thickness analyses, and voxel-based morphometry (VBM), to investigate the neuroanatomical differences between a homogenous group of young adults with autism of average intelligence but delayed or atypical language development (often referred to as "high-functioning autism"), relative to a closely matched group of typically developing controls. The cortical thickness and VBM techniques both revealed regional structural brain differences (mostly in terms of gray matter increases) in brain areas implicated in social cognition, communication, and repetitive behaviors, and thus in each of the core atypical features of autism. Gray matter increases were also found in auditory and visual primary and associative perceptual areas. We interpret these results as the first structural brain correlates of atypical auditory and visual perception in autism, in support of the enhanced perceptual functioning model [Mottron et al. (2006): J Autism Dev Disord 36:27-43].

Figure 1

Group cortical thickness differences. Results from the statistical analysis of cortical thickness data from 15 autistic (AUT) versus 15 typically developing controls (CTR) participants are displayed at each vertex of the surface of a standardized brain (averaged over all participants) in terms of t statistical color maps. Top panel: areas of significant cortical thickness increases (AUT > CTR). Bottom panel: areas of significant cortical thickness decreases (CTR > AUT). aCG = anterior cingulate gyrus, FG = frontal gyri, FusG = fusiform gyrus, HG = Heschl's gyrus, IPL = inferior parietal lobule, LG = lingual gyrus, MedFG = medial frontal gyrus, MOG = middle occipital gyrus, ParaCG = para‐central gyrus, pCG = posterior cingulate gyrus, PostCG = post‐central gyrus, PreCG = pre‐central gyrus, STS = superior temporal sulcus. See Table II for corresponding t values.

Figure 2

Group VBM differences. Results from the statistical analysis of VBM from 15 autistic (AUT) versus 15 typically developing controls (CTR) participants are displayed in the form of t statistical color maps superimposed on either the surface of a standardized brain (e.g., top left brain image) to facilitate the comparison with the cortical thickness results, or on a standardized brain anatomical MRI volume (e.g. top right brain image) (averaged over all participants). Top panel: areas of significant GM increases (AUT > CTR). Bottom panel: areas of significant GM and WM decreases (CTR > AUT). MFG = middle frontal gyrus, PreCG = pre‐central gyri, PostCG = post‐central gyrus, BS = brainstem, CB = cerebellum. See Table III for corresponding t values.