Cortical Thickness Changes in Autism Spectrum Disorders Associated with Age and Social Cognitive Behaviours

Background: There is considerable evidence of atypical brain volume development in individuals with Autism Spectrum Disorders (ASD).  However, little is known about how maturational changes in aspects of cortical morphology, such as cortical thickness contribute to these atypicalities, and how changes relate to diagnostic features of ASD, such as social impairment.

Objectives:  We examined (1) developmental changes in cortical thickness in ASD individuals and typically developing controls, (2) the relation between cortical thickness and Reading the Mind in the Eyes scores between groups, and (3) in the ASD group, the relation between cortical thickness and social scores on the Autism Diagnostic Interview-Revised (ADI-R).

Methods:  Structural Magnetic Resonance Imaging (MRI) scans were obtained from 64 participants, between the ages of 7-17 years. Groups had significantly different IQ scores (ASD: 96.69 ± 17.89 and TD: 115.87 ± 9.58, p<0.05). Based on available data, we included the following number of participants in each analysis: aim (1) 28 ASD and 36 controls, aim (2) 27 ASD and 30 controls and aim (3) 12 ASD. These preliminary analyses were carried out using general linear models, controlling for sex in all analyses, and additionally controlling for age in aims 2 and 3.

Results:  Age-related, cortical thickness differences between groups were observed in middle, medial and superior frontal regions, as well as the precuneus and cuneus.   An interaction between thickness and Reading the Mind in the Eyes scores were found in frontal regions (middle, cingulate), parietal regions (precuneus, postcentral) and an inferior temporal region. Lastly, an association was observed between thickness and symptomatology, with poorer social scores on the ADI-R being associated with thicker cortices in the middle and medial frontal gyri.

Conclusions:  These results show several examples of cortical thickness atypicalities and how it may contribute to social impairments.  Age-related thickness differences in frontal brain regions may contribute to known developmental brain volume atypicalities in ASD. Similarly, the relation between thickness changes in the middle and medial frontal gyri, as well as the fusiform gyrus, and atypical social behaviour is consistent with activation differences in these regions during social emotion tasks. Thus, the findings of the present study suggest that cortical thickness atypicalities are present in ASD and relate to social impairments in ASD.