Cortical Thinning Is Related to Restricted Repetitive Behaviour in Autism Spectrum Disorders

Background: Autism spectrum disorders (ASD) are neurodevelopmental disorders characterised by deficits in two subdomains, social communication and restricted repetitive behaviour as per DSM-V guidelines. Research has suggested that cortical development follows an aberrant trajectory in ASD. Research has shown that brain volume and cortical thickness abnormalities exist in ASD and it has been suggested that these abnormalities may contribute to the traits of ASD.

Objectives: Our research aims to investigate if there is a relationship between measures of cortical integrity (grey and white matter volume, grey and white cerebellar volume, cortical thickness(CT)) and measures of behavioural deficits (social communication deficits (SCD) and fixated interests and repetitive behaviour (FIRB)) in a well-defined ASD sample.

Methods: Freesurfer image analysis software was used was used to generate a cortical surface model to measure brain volume and CT. T-tests and ANOVA were performed to evaluate between group differences on brain volume and CT. Correlation analyses were performed to examine the relationship between SCD, FIRB (Georgiades et al., 2012) and the cortical measures.

Results: The groups did not differ in age (t(102)=-2.46, p=0.806) or IQ (t(102)=-1.792, p=0.076). No significant difference was found between groups in terms of cerebral and cerebellar grey and white matter volume, p>0.05. A significant difference in CT was observed between groups (t(102)=-9.8383, p<0.001) and was observed across all lobes, p<0.001. In the ASD group, RRB was significantly correlated with the right frontal lobe CT (r=-0.375, p=0.035) right parietal lobe CT (r=-0.443, p=0.005) and the left cingulate lobe CT (r=-0.391, p=0.025) corrected for multiple comparisons. SCD was also inversely correlated with the cingulate lobe CT (r=-0.318, p=0.023) and positively correlated with right cerebellar white matter volume (r=0.296, p=0.035) but neither survived correction for multiple comparison.

Results revealed that the ASD group demonstrated reduced cortical thickness in the frontal, parietal, temporal, occipital and cingulate lobes in comparison to the control group. These findings replicate the majority of research demonstrating cortical thinning in ASD. Correlation analyses revealed that restricted repetitive behaviour was inversely related to cortical thickness in the right frontal and parietal lobes as well as the left cingulate lobe, in regions considered necessary for cognitive control and executive functioning.

Conclusions: This study demonstrates that behavioural deficits may be underpinned by structural abnormalities in ASD.