EEG Study of Mirror Neuron Functioning in Infants with Autism Spectrum Disorder

Background: It is quite well known that imitation is impaired in young children with autism spectrum disorder. In primates as well as in humans, imitation has been linked to a group of visuomotor neurons called ‘mirror neurons’, which also fire during action observation. This led to the hypothesis of a dysfunctional mirror neuron system (MNS) in individuals with ASD (Williams et al., 2001). Some support for this hypothesis was found in adults and children, although not all studies found evidence of an impaired MNS in ASD. Research into the MNS with infants remains scarce.

Objectives: Suppression in the EEG mu rhythm band is associated with the MNS activity and was previously investigated in adults and children with and without ASD. In this study, we apply a child-friendly paradigm to investigate mu wave suppression during action observation and action imitation in typically developing infants and infants with a diagnosis or marked characteristics of ASD (age 18-30 months). Following Marchall and colleagues (2002) and Stroganova and colleagues (1999), we defined infant mu wave within the 6-9 Hz frequency range.

Methods: The experiment consisted of 5 blocks (with 5 different objects) and one free play situation (including all 5 objects) during which brain activity was measured on 32 active electrodes. In each block, the infants observed a moving object (object observation condition) and an experimenter performing hand movements (hand movement condition). Subsequently, infants watched (action observation condition) and imitated (action imitation condition) a simple goal-directed action with each object. At the end of the experiment infants were imitated by the experimenter while playing with the objects (free play condition). Hand movement condition and action observation/imitation were counterbalanced between subjects.

Results: 40 infants participated in the study. Preliminary analyses revealed that typically developing infants and infants with (characteristics of) ASD showed significant mu wave suppression on frontal, central, and parietal electrodes during action imitation and play conditions. This suggests that the locations and frequency band were appropriately defined for detecting sensorimotor brain activity. Typically developing infants also displayed mu suppression during the hand movement, and to a lesser extent during the action observation condition. The infants with (characteristics of) ASD showed little mu suppression during the hand movement condition, and none during action observation.

Conclusions: These preliminary results support the presence of a mirror neuron system in typically developing infants, especially during the observation of hand movements. Mirror neuron activity seems to be less pronounced in infants with (characteristics of) ASD.
Full results and conclusions will be presented at the IMFAR meeting.