Cerebral Organization in Young Children with Autism

Background: Abnormalities in cerebral organization have been reported in individuals with autism, but few studies have focused on very young children. Brain volume appears to follow an altered developmental trajectory in individuals with autism, yet the timing and nature of early overgrowth has not been adequately examined. Aberrant sulcal organization and connectivity patterns have also been reported in older individuals with autism, but extension of these findings to younger children has not been fully explored.

Objectives: To evaluate multiple aspects of cerebral organization in a large sample of 2-4 year old children with autism spectrum disorders. Analyses include total cerebral volume and cortical sulcal organization, a putative measure of connectivity.  This study was carried out in the context of the M.I.N.D. Institute’s Autism Phenome Project.

Methods: Structural MRIs were acquired in 107 children (49 autism [AU], 24 autism spectrum disorders [ASD], 34 typical development [TD]), ages 27-56 months (mean 40 months). Diagnostic instruments included the Autism Diagnostic Observation Schedule – Generic (ADOS-G) and the Autism Diagnostic Interview – Revised (ADI-R). Children with typical development did not have any siblings with autism or any known developmental, neurological, or behavioral problems. Additional exclusionary criteria were limited to those with physical contraindications to MRI.  Volumetric analyses included measurements of the total cerebrum. Surface-based morphometry was used to generate sulcal depth maps to evaluate cortical folding patterns.

Results:  In males, age was correlated with total cerebral volume in the TD group (r = .49, p = .01) but not in the AU (r = -.02; p = .9) or ASD (r = = .4, p = .1) groups.  In males 27-42 months of age, total cerebral volume was significantly enlarged in the AU group relative to the TD group (p = .03). The ASD group did not differ significantly from either the AU or the TD group.  Preliminary analyses of sulcal depth maps suggest that children with AU and ASD have abnormalities in sulcal organization in superior temporal regions as well as the intraparietal sulcus; areas typically associated with biological motion and attentional control respectively.

Conclusions: Preliminary data show that boys with autism spectrum disorders do not have typical age related growth in total cerebral volume. Brain enlargement is present in children with autism under the age of 3.5 years. Regional abnormalities in sulcal organization are also present in young children with autism, suggesting an abnormal pattern of connectivity in functionally relevant brain regions early in development.