Patterns of brain functional connectivity within neurocognitive subtypes of autism spectrum disorder
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Autism spectrum disorder (ASD) is a heterogeneous neurodevelopmental disorder. There have been increased efforts to identify meaningful subtypes of ASD based on a variety of measures (e.g., behavioral symptoms, genetic information, etc.). Elucidation of homogenous subtypes may lead to clearer understanding of underlying brain functioning and etiology of ASD. A recent exploratory study aimed to determine whether neuropsychological test data could be used to parse a group of individuals with high-functioning ASD into homogenous “subtypes” based on unique neurocognitive profiles (Wagner, 2014). Results of that study were promising and suggested the emergence of 3 clusters. This subset of individuals with ASD was successfully parsed into smaller more homogenous subgroups based on unique neurocognitive profiles driven by performance on measures of reasoning, receptive language, and learning/memory. Thus, corresponding brain regions were selected for further study in order to explore potential underlying differences in brain functioning across identified clusters. Resting state functional connectivity magnetic resonance imaging (rs-fcMRI) is an emerging neuroimaging tool used to examine functional correlations among spatially distinct brain regions. Previous rs-fcMRI studies examining individuals with ASD have found evidence for altered connectivity; however, results have been inconsistent. Inconsistencies may be related to the heterogeneous nature of ASD and underlying differences in potential neurocognitive subtypes within ASD samples. The current study aimed to extend preliminary research by comparing patterns of functional connectivity of frontal brain regions, Wernicke’s area, and hippocampal regions across previously identified clusters to examine potential differences in underlying brain function. Results indicated The ASD subgroup with above average reasoning and language skills had increased frontal functional connectivity in comparison to other ASD subjects and controls, as well as increased posterior superior temporal gyrus connectivity in comparison to other ASD subjects. The ASD subgroup with below average learning and memory had decreased hippocampal functional connectivity in comparison to controls. However, when ASD subgroups were combined, there were no differences in functional connectivity between ASD and controls. Thus, ASD may be related to unique alterations in functional connectivity networks, however meaningful subgroup differences are easily masked by sample heterogeneity. Identification of neurocognitive profiles may provide diagnostic utility both within the spectrum and between ASD and other disorders. Diagnostic clarification in the form of a “neurocognitive subtype” could provide useful information about cognitive strengths and weaknesses and directions for treatment and intervention planning. Further delineation of the ASD spectrum, including variations in cognitive profiles and related underlying brain networks, may reveal important differences in underlying etiology and response to treatment.