Atypical Lateralization of Language and Face Processing in Autism Spectrum Disorder

Autism spectrum disorder (ASD) is characterized by persistent deficits in communication and social interaction, as well as repetitive behaviours and restricted interests. Language and face processing are areas of domain-specific dysfunction impacting social interaction in ASD. Brain function associated with these cognitive domains is typically lateralized across the cerebral hemispheres, such that language and face processing are dominant within the left and right hemispheres, respectively. Furthermore, the degree of lateralization is related to behavioural proficiency in both domains. Converging evidence suggests that the development of lateralization in these separate domains is typically interrelated. Neuroimaging literature demonstrates reduced leftward lateralization of language in ASD, but the existing literature on face processing is inconsistent. Mixed findings are partly due to discrepancies in how regions of interest (ROIs) are localized for neuroimaging analyses. The present work aims to test the hypothesis that ASD is related to atypical lateralization of both language and face processing. First, a quantitative fMRI meta-analysis was conducted to resolve inconsistencies in the literature by identifying the most reliable, concordant patterns of differences in language and face processing in the brain associated with ASD across previous fMRI studies. The findings of the meta-analysis were then used to inform a rigorous analysis of category-related brain activation using individually localized ROIs and task-related fMRI data. However, the question remains regarding whether brain activation differences demonstrate a sustained, fundamental difference in the way language and faces are processed in the brain, rather than reflecting moment-to-moment differences in attention to these stimuli, motivating the final analysis of intrinsic functional connectivity between category-related brain regions. The findings from the meta-analysis, task-related fMRI analyses, and RSFC analysis of intrinsic functional connectivity converged, demonstrating that ASD is indeed related to reduced functional specialization and hemispheric lateralization of both language and face processing, particularly in posterior lateral temporal cortex. This is an important contribution to the mixed existing literature, and further demonstrates the importance of individual ROI localization when studying neurodiverse populations. Atypical development of hemispheric asymmetry for language and face processing in posterior lateral temporal cortex might be a fundamental factor underlying the behavioural presentation of ASD.