Understanding the “How” and “Why” of Actions in Autism Spectrum Disorders: The Role of Mirroring and Mentalizing Systems

Background:  Human beings are often engaged in interpreting the means (how) and intent (why) of others’ actions. It has been proposed that understanding the intention of others’ actions is accomplished by means of an automatic motoric simulation (Gallese and Goldman, 1998), possibly mediated by mirror neuron system (MNS) activity in the ventral premotor cortex and inferior parietal lobule (Rizzolatti et al., 1998; Gallese et al., 2004). In contrast to this, others argue that mentalizing recruits regions outside the motor system, such as the temporoparietal junction (TPJ), superior temporal sulcus (STS), and medial prefrontal cortex (MPFC) (Saxe, 2006; Frith & Frith, 2003). Recently, it has been found that these two systems may be complementary in understanding actions (de Lange et al., 2008). While impairments in both systems have been reported separately in people with autism spectrum disorders (ASD), to our knowledge, they have not been investigated in conjunction. The present study addresses the validity of mirroring and mentalizing hypotheses in autism in understanding the means and intent of actions.

Objectives:  The main objective of this functional MRI study was to investigate the nature of mirror neuron and mentalizing system response to interpreting the how and why of actions in high-functioning adults with ASD. 

Methods:  fMRI data was acquired from 5 high-functioning adults with ASD and 5 typically developing controls (data collection in progress) while they made action and intention judgments about a series of static images of a model using household objects (adapted from de Lange et al., 2008). The participants’ task was to view the model’s action and determine whether the means (how the action was carried out) or intent (the model’s goal) of the action was ordinary or unusual. The stimuli were presented in blocked design and the data were acquired on a Siemens 3T scanner and analyzed using SPM8.

Results:  The results are as follows: 1) ASD participants showed significantly reduced response in bilateral TPJ and left inferior frontal gyrus (IFG), relative to controls, while inferring the model’s intent; 2) While detecting unusual means the ASD group activated significantly lesser, relative to controls, in bilateral IFG and left angular gyrus; but showed greater response in right supramarginal, bilateral supplementary motor, and right superior MPFC; and 3) Paired samples t-tests on the behavioral data determined no significant differences between the groups for accuracy and reaction time for all experimental conditions.

Conclusions:  Our finding of TPJ and IFG activation in controls for inferring the model’s goal underscores the complementary roles of the mirror neuron and mentalizing networks for inferring intentions.  That the means condition also activates the IFG in controls is suggestive of the role of the IFG for the simulation of actions and intentions, whereas the TPJ is likely additionally recruited for interpretation of the intentions. Despite finding no behavioral differences between autism participants and controls, our participants with autism showed reduced response in these regions while processing the intent of actions, indicating a possible use of an alternate cortical route in individuals with autism when interpreting others’ actions.