EEG Mu Wave Attenuation in Broader Phenotype ASD

Background:  

The Broader Autism Phenotype (BAP) refers to autistic traits that may be qualitatively similar but expressed to a lesser degree than fully developed impairments associated with autism (Piven et al., 1997). Electrophysiological measures have been useful in the exploration of the BAP, highlighting differences in parents of children with ASD, such as impairments in face processing (Dawson, Webb et al., 2005). Previous EEG research has evidenced dysfunction of an execution-observation matching system in individuals with ASD. The attenuation of mu wave (spectral power falling within the 8-13 Hz frequency range), has consistently been observed during the execution-observation of human movement (e.g., grasping). Bernier et al. (2007) and Oberman et al. (2005) found reduced mu rhythm attenuation during observation, but not execution, of biological motion for individuals with ASD compared to a TD group, suggesting an execution-observation system dysfunction in ASD. However, findings have been inconsistent (Raymaekers et al, 2009). It is hypothesized that if reduced mu attenuation were a component of the BAP, parents of children with ASD would fail to show attenuation of the mu wave during the observation of a biological action, compared to parents of TD children.

Objectives:  

This study aims to examine if differential EEG activity in execution-observation matching, as evidenced by reduced mu wave attenuation, is observed in parents of children with ASD.

Methods:  

EEGs were collected during Resting, Observation and Execution of a simple hand-grasp motion from 84 parents of children with ASD and 31 parents of non-ASD children. Mu rhythm was defined as the power in the 8-13 Hz band among a cluster of eight electrodes over the central right and left hemisphere.  Degree of mu attenuation was quantified as the log transform of the ratio of the power in the Observe and Execute conditions compared to the Resting condition. 

Results:  

Preliminary analysis confirmed that there was no difference between resting mu rhythm between groups (F (1, 113) = .7, p = n.s.).

When observing a biological movement, mu wave was significantly attenuated in both groups, replicating previous findings of an execution-observation matching system in individuals with TD, and extending these findings to parents of individuals with ASD (TD t= -5.24, df = 30, p<.001; ASD t= -8.14, df = 83, p<.001). There was no significant difference in mu power between groups in the observe condition (t = -0.39, df = 113, p = n.s.)

Conclusions:  

The lack of differences between groups in the attenuation of spectral power in the mu rhythm when observing grasping actions suggests intact functioning of the execution-observation matching system in parents of children with ASD.  Our findings suggest that differential mu wave activity during the observation of biological movement likely is not a component of the broader autism phenotype, but is rather specific to individuals with ASD. It is possible that given the small sample sizes, power may be an issue for these analyses. Additional analyses will examine the relationship between the BAP and mu attenuation in the parent group.