Brain Mechanisms for Processing Social Approach: Relationships to Autistic Traits

Background: Disrupted social perception and cognition is a core feature of autism spectrum disorder (ASD). Social interactions begin with the approach of one person towards another; biological motion (eye, face or whole body motion) typically conveys this intent for social engagement. Researchers have documented ASD-related disruption in the brain mechanisms for perceiving the intent for social engagement (vis-à-vis direct vs. averted gaze). However, the perception of approaching versus passing full body biological motion has never been directly studied. Further, while brain mechanisms for biological motion perception have been implicated in ASD (Kaiser et al., 2010, PNAS), no study to date has used functional magnetic resonance imaging (fMRI) to specifically examine the relationship between autism and the perception of approaching versus passing human motion.

Objectives: We sought to characterize the brain mechanisms for processing approaching versus passing biological motion in typically developing adults and to examine the relationship between autistic traits and such mechanisms. This study also serves to develop a task to investigate this neural circuitry in individuals with autism.

Methods: During an fMRI scan, 19 typically developing adults (mean age = 23.80 ± 2.85) viewed masked point-light displays of an emotional human figure either approaching (walking towards) or passing (walking left-to-right or right-to-left). Participants viewed each stimulus (3 second duration) in a pseudo-random order and then reported (2 second query) with Y/N button-press whether they detected a walker in a masking cloud of dots. There were 18 stimuli, each shown twice over the course of the experiment. Participants also completed the Autism-Spectrum Quotient (AQ).

Results: At the behavioral level, participants exhibited equivalent detection (accuracy and reaction time) of approaching and passing walkers. However, an RFX GLM (q = .001, k = 40) identified brain regions that were differentially responsive to approaching versus passing walkers. We examined the relationship between AQ scores and beta values in each of the regions identified in the above contrast. AQ scores (ranging from 3-20) negatively correlated with the response to approaching walkers in the right temporoparietal junction (r = -.474, p = .020) and the left cerebellar tonsil (r = -4.14, p = .039).

Conclusions: We conducted an fMRI study that identified brain regions for processing approaching and passing human locomotion and further discovered that autistic traits predict brain response to socially engaging stimuli in two brain regions. These regions, the left cerebellar tonsil (Sokolov et al., 2010, Cerebral Cortex) and the right temporoparietal junction (Saxe, 2006, Current Opinion in Neurobiology) play a key role in action observation and other social cognition tasks relating to social engagement. This study illustrates a tight coupling of autistic traits and disrupted mechanisms for fundamental aspects of social cognition (i.e., the critical detection of intent for social engagement). Future studies will examine such mechanisms in children with autism.