Functional Neuroimaging Correlates of Intentional Biological Motion Processing in Unaffected Siblings of Children with ASD

Background:  A network of brain regions implicated in the processing of social stimuli has been investigated in typically developing children and those who have an autism spectrum disorder (ASD) to identify neural mechanisms of social behavior. Doing so improves our ability to use quantitative endophenotypes to characterize individuals beyond a categorical diagnosis. Moreover, investigating social brain activity in unaffected siblings of children with ASD could uncover brain mechanisms that compensate for inherited risk. For example, unaffected siblings showed unique patterns of brain activity in the right posterior superior temporal sulcus (pSTS) when they viewed point-light displays of human biological motion relative to scrambled motion. In action perception, neurotypical children and adults, but not children with ASD, showed preferential activation in the pSTS to human biological actions that are incongruent with a prior displayed intention (positive or negative emotion). 

Objectives: To investigate the functional activation of social brain regions implicated in action perception in unaffected siblings of children with ASD, relative to typically developing children.

Methods: Twenty-two unaffected siblings of children with ASD (age = 12.58, SD = 2.43) and a control group of twenty-two typically developing children who did not have a brother or sister with ASD (age = 11.63 years, SD = 1.85) were scanned on a Seimens 3T MRI scanner. The groups were matched on gender (8 females) and there were no significant differences in age or T-scores on the Social Responsiveness Scale (p = 0.15 and 0.29 respectively). Average SRS scores were below the threshold for mild ASD (49.36 for siblings, 45.55 for controls). All participants were shown a 6’16’’ paradigm consisting of a human actor who displayed positive or negative affect towards one of two cups on the screen. The actor then picked up one of the two cups in either a congruent or incongruent fashion. Congruent trials matched the displayed intention; the actor reached for the same cup if she displayed positive affect or the opposite cup if she displayed negative affect. Conversely, action did not match intention in the incongruent trials. An empirical region-of-interest in the right pSTS was created with an activation-likelihood estimation meta-analysis, in which published co-ordinates are used to create a probabilistic map of regions most likely to be active to a chosen class of stimuli. Waveforms from this region were extracted, and response was defined as activation at 10 seconds after stimulus onset relative to initial activation.

Results: Typically developing children were found to significantly differentiate incongruent and congruent actions in meta-analytically defined pSTS (paired t(21) = -3.6802, p = 0.001392), replicating previous findings. Unaffected siblings, however, did not differentiate the two conditions (paired t(21) = 0.6162, p = 0.5444).

Conclusions: These findings lend further evidence to the hypothesis that brain activations provide information that transcends diagnostic categories. Specifically, we show that unaffected siblings display atypical action perception processing despite showing typical levels of social cognitive behavior, as measured by the SRS. Understanding the neural mechanisms of social cognition in siblings could shed light on the influences of genetic risk for ASD upon the brain.