Brain Responses to Anthropomorphism and Perception of Actions in Autism

Background:  Anthropomorphism or the attribution of human characteristics (motivation, intention, and emotion) to non-human agents has been associated with the activation of mentalizing areas such as the posterior superior temporal sulcus (pSTS), the medial prefrontal cortex, and the anterior cingulate cortex (Chaminade et al., 2007). Individuals with autism have demonstrated difficulty in social attribution along with reduced activity in mentalizing regions (Kana et al., 2009). In addition, individuals with autism also showed diminished response to biological motion in regions like the pSTS (Pelphrey et al., 2005) as compared to typically developing peers. The present study examined brain responses associated with anthropomorphism and mentalizing in autism.  Using stimuli that elicit different levels of anthropomorphism, we expect that human social motion will elicit more activation in mentalizing brain areas in controls than non-human motion, while participants with autism will have altered brain response for socially meaningful motion. 

Objectives:  The purpose of this fMRI study was to investigate the role of pSTS and other mentalizing regions in motion processing in the context of anthropomorphism.

Methods:  fMRI data were acquired from 5 high-functioning adults with autism and 6 typically developing controls (data collection in progress) while they viewed short animations of pairs of shapes (triangles) and stick figure characters engaged in random and socially meaningful movements. The average length of an animation was about 10 seconds. The participants’ task was to view the animations and judge whether the characters’ motion was social (intentional/goal-directed) or random. The stimuli were presented in an event-related design and data were acquired on a Siemens 3T scanner and analyzed using SPM8.

Results:  The main results are as follows: 1) This study elicited strong responses in bilateral pSTS to movements of shapes and stick figures in both groups of participants; and 2) While observing social movement from shapes to stick figure characters, the control participants recruited a set of frontal regions, including the inferior frontal gyrus. However, the frontal activation was absent in participants with autism and their response was restricted to more posterior brain regions, like the extrastriate body area and the temporoparietal junction.

Conclusions:  Our results support previous findings of the role of the pSTS and the prefrontal cortex for anthropomorphism (Chaminade et al., 2007). Inferior frontal cortex in control participants seems to play a vital role as the anthropomorphism increased from shapes to humans, a trend not seen in autism. These findings underscore the role of the pSTS in biological motion, with the inferior frontal area more specific to human social motion. We did not find differential activation in our autism participants between social shape and social human movements. This suggests that anthropomorphism may not be a key factor in the way participants with autism process these movements. This is potentially significant for people with autism in real life social interactions.