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Guy. M., Richards, J.E. & Roberts, J.E. (2018). Cortical Source Analysis of ERP Responses to Faces in Etiologically Distinct Groups of Infants at High-Risk for ASD. INSAR, Rotterdam, Netherlands, May 2018.

Background: The aim of this study was to examine cortical sources active during face processing in two groups of infants at high-risk of autism spectrum disorder (ASD). Event-related potentials (ERPs) associated with specialized face processing (i.e., N290) were measured in response to faces and toys across high-risk groups, including infant siblings of children with ASD (ASIBs) and infants diagnosed with fragile X syndrome (FXS), as well as low-risk control (LRC) infants (Guy, Richards, Tonnsen, & Roberts, 2017). All groups demonstrated greater amplitude N290 responses to faces than toys. Infants with FXS displayed the greatest amplitude N290 and most differentiated responses to faces and toys. Objectives: Cortical source analysis was utilized to investigate whether group differences in ERP responses corresponded to different levels of activation in brain regions most closely linked to specialized face processing or differences in areas active during face processing. Methods: Twelve-month-olds were recruited for this study, including 21 ASIBs, 15 infants diagnosed with FXS, and 21 LRC infants. All participants completed an ERP experiment including face and toy stimuli. Structural MRIs were collected from a subset of the participants and a group-specific (ASIB, FXS, or LRC) average head model was used to complete source analysis in infants that did not contribute their own MRI (Guy, Richards, & Roberts, 2017). Realistic head models were created from the MRIs. Current density reconstruction (CDR) of the N290 was calculated to examine activation in regions of interest (ROIs) believed to be relevant to face processing. CDR activity was analyzed in an ANOVA including the factors of participant group, stimulus type, and ROI. Results: There was a significant main effect of stimulus type, F(1, 55) = 21.47, p < .0001, reflecting greater activation to faces than toys. There was a stimulus type by ROI interaction, F(17, 935) = 4.91, p < .0001, due to higher levels of activation in response to faces than toys in the middle fusiform gyrus and nearby temporal and occipital brain areas. Additionally, an interaction of group, stimulus type, and ROI was observed, F(34, 935) = 1.45, p = .0465. As shown in Figure 1, LRC infants demonstrated greatest levels of activation in response to faces in brain areas most closely linked to specialized face processing (i.e., middle fusiform gyrus, anterior fusiform gyrus, parahippocampal gyrus, lingual gyrus), but infants with FXS were the only participant group to display higher levels of activation to faces than toys across all ROIs examined. Conclusions: The results provide evidence for unique patterns of neural activation during face processing across infants at high- and low-risk for ASD, and across distinct high-risk groups. All infants demonstrated greater activation to faces than toys in brain areas most associated with specialized face processing, but only infants with FXS consistently displayed higher levels of activation to faces across a broad range of areas analyzed. These results indicate that greater amplitude N290 responses observed in infants with FXS are due to an increased area of activation during face processing, rather than greater activation in specialized face processing areas.