The Mirror Neuron System as Evidenced by Attenuation of EEG Mu Rhythm and Social Aptitude in Autism Spectrum Disorders

Background: The mirror neuron system (MNS) activates in response to observing and executing a motor action. Though originally observed via single neuron recording in monkeys (Rizzolatti et al., 1996), it is evidenced in humans through the attenuation of the mu rhythm observed via electroencephalography (EEG).  This system is suggested to be the biological basis of imitation (Rizzolatti & Craighero, 2004). Some theories place imitation at the core of the developmental course of ASD (Rogers & Pennington, 1991),  and MNS dysfunction has been demonstrated in ASD populations (Oberman et al., 2005, Bernier et al., 2007).

Objectives: To examine mu attenuation and its relationship to autism symptomology.

Methods: EEGs were collected during the observation of biological movement (simple grasping motion) from a sample of adults with an autism spectrum disorder (ASD, N=15) and typical development (TYP, N=14). Ratio of the power in the 8-13 Hz band recorded from 16 central electrodes at the C3 and C4 sites during observation relative to resting power was calculated and log transformed as a measure of mu attenuation. A caregiver report of autism symptomology on the Autism Spectrum Quotient (AQ) was collected and the relationship between mu attenuation and autism symptomology was calculated. 

Results: Analysis reveals a significant correlation between mu attenuation and scores on the social skills subscale of the Autism-Spectrum Quotient (AQ) in the AUT group (R2=.551, p<.03), most pronounced in the left hemisphere (R2=.592, p<.02). No significant correlations were found between mu attenuation and other AQ subscales. Additionally, no significant correlations were observed in the TYP group.

Conclusions: Our results are consistent with recent findings extending the involvement of the MNS beyond motor-execution/observation to include social abilities. Other studies have implicated the MNS in the interpretation of context and intention (Iacaboni et al., 2005), as well as the interpretation of social stimuli (Oberman et al., 2007). Our findings further demonstrate a connection between the mirror neuron system and imitation and its consequence in social aptitude.