Visuo-Spatial Function Pertaining to the Parietal Region Compared to Verbal Function within the Autism Spectrum

Background: Although visuo-spatial function and verbal function are two separate parts of cognition, they are frequently used concurrently when language is used to make reference to spatial objects. The atypical processing of low-level visuo-spatial function and verbal function found in autism has lead researchers to study the interaction between the two. It has been suggested that atypical neural connectivity may account for visuo-spatial processing abnormalities in autism. Objectives: Our goal was to understand more about visuo-spatial processing in autism relative to typical development in these three ways. First, we looked at the discrepancies between visuo-spatial function and verbal IQ between the two groups. Second, in the brain volume and cortical thickness of the parietal regions of autistic brains compared to controls. Finally, we looked at the correlation between brain structures and visuo-spatial function. Methods: 3T MRI T1-weighted images were obtained from 20 high functioning autistic adult males (mean age= 22.8) group matched by age and head circumference to 19 typically developing control male adults (mean age=22.0). A diagnosis of autism was obtained using the ADI and the ADOS. Visuo-spatial function was measured by using the WASI Matrix Reasoning subtest and the Test of Memory and Learning Abstract Memory subtest. Verbal function was measured by using Verbal IQ of the WASI. Parietal regional brain volumes and cortical thickness were extracted using FreeSurfer software. The comparison was done by two sample t-test, ANOVA and linear regression. Results: While controlling for age, significant autism-control differences between verbal function and visuo-spatial function were found (p range= .003-.006). Significantly decreased cortical thickness was found in the autism group relative to controls in the following parietal subregions: inferior parietal (p= .007), parietal inferior angular (p = .041) and precuneus (p = .021). Significant positive correlations were found between measures of visuo-spatial function and cuneus and parietal regions in the autism group only (p ranges = .456 to .596). Within the controls, negative correlations were found between the same brain measures and visuo-spatial tests (p ranges = -.475 to -.645). Conclusions: We have found statistically significant differences between groups in visuo-spatial function compared to verbal function. The differences found in the cortical thickness of the parietal lobe may indicate abnormal cortical development in individuals with autism. In brain regions found to be important in visuo-spatial function individuals with autism may benefit from increased cortical thickness whereas this relationship may not found within controls.