Mirror Neuron System Activation in Autism in Reponse to Transitive and Intransitive Actions

Background: An apparent conflict is present in current thinking about the role of Mirror Neuron System (MNS) functioning in autism. The conflict involves findings that suggest a global MNS abnormality in autism, and findings that suggest there is preserved MNS functioning based on evidence of understanding of other’s actions and intentions in ASD, which stimulates MNS in animals.

Objectives: The goal of this study was to examine mu wave suppression through EEG recording (power in the 8-13Hz band recorded over motor cortex), as an index of MNS activation, to the observation of actions on objects (transitive actions) and body movements (intransitive actions) in children with autism.

Methods: Participants in the current study were 9 children and adolescents with high-functioning autism (8 male, 1 female) between the ages of 9 and 16 years, and 9 children and adolescents with typical development matched on chronological age, language level, Performance IQ, and gender proportion. Continuous EEG was acquired from a customized Falk Minow cap with spherical 124 equidistant scalp electrodes arrangement using a 140 channel Neuroscan Synamps2 system and digitized at 1 kHz while participants were viewing videos of transitive actions involving action and intention understanding and intransitive actions.  The experiment was run in 4 blocks of 50 stimuli each with stimulus type randomized. Each video segment was followed by a randomized intertrial interval of 4-7 seconds to prevent anticipation of the stimuli. 
Results: When presented with transitive actions children with autism showed mu suppression similar to the control group in both the central and the parietal areas. However, they showed larger suppression to the presentation of intransitive actions in both the central and the parietal areas. Only typical children showed larger mu suppression in the transitive condition in comparison to the intransitive condition. Neither group showed mu suppression in the occipital area.

Conclusions: As predicted, the autism group demonstrated typical mu wave suppression during the observation of transitive actions, a finding that is not explained by the hypothesis of a global MNS dysfunction in autism. The abnormal pattern identified in autism did not reside in a lack of activation but rather in an excess, as shown by larger mu suppression during the presentation of intransitive actions, and a lack of modulation across functions (transitive vs. intransitive), as shown by similar suppression between the presentation of transitive and intransitive actions in autism.