Disruptions in the mirror neuron system (MNS) have been suggested to play a key role in the core social deficits observed in autism spectrum disorders (ASD). However, recent empirical studies have conflicting results with some supporting a dysfunction in this system and others not. These discrepant findings may be accounted for by factors such as population heterogeneity, differences in age of the various samples, lack of power, particular stimuli used etc.
Objectives:
Given the discrepant findings in the literature and the importance both clinically and theoretically to understand factors mediating the functioning or dysfunction of the mirror neuron system in ASD, we conducted a direct exploration of the development of mu rhythm suppression with age in individuals with ASD in ages 6-17 by pooling data across four previously published studies (Oberman et al., 2005; Oberman et al., 2008; Pineda et al., 2008; and Raymaekers et al., 2009).
Methods:
Raw data were obtained with permission from the corresponding authors of four published datasets. All of the studies included in this analysis had almost identical methodology for data collection and analysis. Mu suppression, as indexed by the ratio of mu power over central electrodes (C3 and C4) during action observation or execution divided by mu power during baseline, was calculated for each individual participant. We calculated Pearson correlation coefficients in order to quantify the relationship between mu suppression and age across all subjects as well as for each group individually. Correlation coefficients were also directly compared between the two groups using the calculation for the test of the difference between two independent correlation coefficients (Preacher, 2002) in order to evaluate whether or not the relationship between age and mu suppression differed between the ASD and control groups.
Results:
We found a significant correlation between age and mu suppression in response to the observation of actions, both for individuals with ASD and typical individuals. This relationship was not seen during the execution of actions. Additionally, the strength of the correlation during the observation of actions did not significantly differ between groups.
Conclusions:
These results suggest that developmental changes to the systems underlying mu suppression in response to observation of actions are independent of diagnosis. Additionally, that mu suppression in response to executed actions does not change over the age range from 6 to 17. The results provide evidence against the argument that mirror neuron dysfunction improves with age in individuals with ASD and suggest, instead, that a diagnosis-independent developmental change may be at the root of the correlation of age and mu suppression during the observation of actions.