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Description
Core features of Autism Spectrum Disorders (ASD) include deficits in sociocommunicative behavior and the occurrence of stereotypical and repetitive behaviors. Current research suggests that the behavioral features of ASD may be indicative of atypical patterns of connectivity and possibly reduced functional differentiation of cortex. In several studies, participants with ASD displayed atypical activation in the inferior frontal gyrus (IFG), which is involved in a variety of functions including language processing, motor imagery and planning, imitation, working memory, and response inhibition. Such abnormal activation may reflect atypical connectivity patterns and abnormal differentiation within IFG. Based on previous findings, the current study tested four hypotheses: (1) Specialized IFG subregions would be identified based on differential functional connectivity patterns in the TD group, (2) the differentiation within these subregions would increase with age in the TD group, (3) this differentiation would be reduced in ASD, compared to matched TD participants, and (4) within the ASD group, severity of the disorder would be associated with reduced differentiation. Participants included a total of 47 children ages 8-19 years old, 21 individuals with ASD, and 26 typically developing (TD) individuals, matched for gender, age, and IQ. We identified three subregions within IFG in each hemisphere, using a data driven approach (including singular value decomposition and principal component analysis). Seeds were created for bilateral frontal operculum/insula, pars triangularis, and the inferior frontal sulcus. Functional connectivity magnetic resonance imaging (fcMRI) was then used to examine the whole brain connectivity of each subregion and to evaluate the functional differentiation in spatial and temporal domains across the IFG subregions. We further computed correlations of spatial and temporal differentiation indices with age and with diagnostic scores (reflecting severity of ASD). As hypothesized, individual seeds had distinct connectivity patterns, reflective of specialized networks. fcMRI analysis showed that the seed located in left frontal operculum/insula had connectivity primarily with regions associated with attentional networks, while the seed in pars triangularis was strongly connected with classic language networks and the inferior frontal sulcus displayed connectivity with regions involving executive functions and working memory. These connectivity patterns were fairly consistent, although less extensive, in homotopic right hemisphere regions. The ASD group displayed overall greater connectivity, with more diffuse regional patterns, than the TD group. In the TD group, spatial differentiation of subregions was positively correlated with age in both hemispheres. However, this effect was not found for temporal differentiation. Overall, the ASD group showed significantly lower differentiation than the TD group in the left hemisphere. This difference was not detected in the right hemisphere. Hypothesis 4 was not supported by the findings, as severity of ASD was not correlated with differentiation. These results indicate that in high-functioning children and adolescents with ASD, IFG may be characterized by both reduced segregation and atypical connectivity patterns, including widespread overconnectivity.
