Animacy and Intentionality in the Mirror Neuron System in the Broader Autism Phenotype

Background: Research in non-human primates first revealed the existence of single neurons activated in response to performance of an action and observation of the same action. Subsequent neuroimaging studies in humans provide strong evidence for a similar action-perception system (APS) in humans.  Electrophysiological brain recordings reveal that rhythmic activity in the mu range (8-13 Hz) reflects the synchronous firing of motor neurons at rest, and attenuation of this rhythm in the absence of motor movement is a reliable marker of APS activity. Dysfunction in this neural circuitry has been observed in ASD; individuals with ASD exhibit typical mu attenuation during motor actions but reduced attenuation during action observation. Based on these findings, atypical function of this brain system has been speculated to contribute to the neuropathology of the disorder. Several studies have investigated the modulatory influences of the intentionality of observed actions (i.e., goal-oriented vs. non-goal-oriented actions), as well as the animacy of the performer of the observed action (i.e., human versus humanoid robot), although it remains unclear to what degree and in what direction these factors influence activity in the APS.

Objectives: This study investigated (a) the modulatory influence of intentionality and animacy, as well as (b) the level of autistic traits, on APS activation as revealed by electrophysiological indices. 

Methods: 20 typically developing adults participated in this study. Participants were pre-selected for high (H-AQ, N=10) or low (L-AQ, N=10) levels of autistic traits with the Autism Spectrum Quotient. EEG was recorded using a 128 channel HydroCel Geodesic Sensor Net while participants viewed a novel series of short videos displaying four conditions varying performer animacy and intentionality: 1) human hand, goal-directed; 2) human hand, non-goal-directed; 3) robot hand, goal directed; 4) robot hand, non-goal-directed. Mu power (8-13 hz) was computed over central electrodes and log ratios (video stimuli: baseline) were compared between the four conditions.

Results:  We predict that, across participants, both animacy and intentionality will modulate APS activity such that Condition 1 > Condition 2 > Condition 3 > Condition 4. We expect that the H-AQ group will exhibit reduced mu attenuation overall and reduced differentiation among conditions, indicating less sensitivity to animacy and intentionality. Though data collection is ongoing, preliminary analyses concord with these predictions. 

Conclusions: This is the first study to (a) apply EEG to investigate the effect of animacy and intentionality on mirror neuron activation and to (b) analyze these effects in the context of the broader phenotype of autism. Our novel stimulus set eliminates confounds between familiarity and intentionality; confirmation of predictions will inform our understanding of APS involvement in empathy, theory of mind and in the broader autism phenotype.