Human mirror neurons have theoretically been linked to imitation, language, empathy, and other social-communicative skills. Since most of these skills are impaired or delayed in children with autism spectrum disorder (ASD), it has been hypothesized that the mirror neuron system may be dysfunctional in individuals with ASD. Although this ‘broken mirror’ hypothesis was confirmed in some studies, others found evidence for a normally functioning mirror neuron system in ASD. Although mirror neurons are highly influenced by (social and motor) experience, until now no studies were conducted with infants or young children with ASD. It may however be expected that while children with ASD grow older, the limited amount of social information they process may hamper the development of a fully functional mirror neuron system.
To investigate mirror neuron functioning in typically developing young children, in young children with a diagnosis of ASD, and in young children with an elevated risk for ASD (defined by having at least one older sibling with ASD).
We used EEG mu suppression as an index of mirror neuron functioning. Sufficient artefact-free EEG data was obtained from 33 typically developing children, 24 children with ASD and 25 siblings of children with ASD (mean age = 42 months, SD = 15). Mu suppression was measured in three conditions, relative to a baseline. In these conditions, the children 1) observed intransitive hand movements, 2) observed actions on objects or 3) were invited to imitate the actions on objects. During the baseline, they only observed moving objects.
On the central electrode positions C3 and C4, we measured significant mu suppression in the three conditions, in all three groups. A repeated measures MANOVA showed no main effect of group and no group*condition interaction effect. During the imitation condition, the mu suppression in all three groups tended to be stronger than in the other two conditions. Although mu suppression in all three conditions was strongly intercorrelated, there were no correlations between mu suppression on the one hand and child characteristics such as age, language level, imitation score and autism symptoms on the other hand.
In young children with or at risk for ASD, we found a functional mirror neuron system, as measured by mu suppression. Together with the absence of correlations between mu suppression and social communicative abilities, these results do not provide evidence for the ‘broken mirror’ hypothesis.
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