Parieto-frontal circuits during observation of hidden and visible motor acts in children. A high-density EEG source imaging study.

Several studies showed that in the human brain specific premotor and parietal areas are activated during the execution and observation of motor acts. The activation of this premotor-parietal network displaying the so-called Mirror Mechanism (MM) was proposed to underpin basic forms of action understanding. However, the functional properties of the MM in children are still largely unknown. In order to address this issue, we recorded high-density EEG from 12 children (6 female, 6 male; average age 10.5, SD ±2.15). Data were collected when children observed video clips showing hands grasping objects in two different experimental conditions: (1) Full Vision, in which the motor act was fully visible; (2) Hidden, in which the interaction between the hand and the object was not visible. Event-related potentials (ERPs) and topographic map analyses were used to investigate the temporal pattern of the ERPs and their brain source of localization, employing a children template of the Montreal Neurological Institute. Results showed that two different parieto-premotor circuits are activated by the observation of object-related hand reaching-to-grasping motor acts in children. The first circuit comprises the ventral premotor and the inferior parietal cortices. The second one comprises the dorsal premotor and superior parietal cortices. The activation of both circuits is differently lateralized and modulated in time, and influenced by the amount of visual information available about the hand grasping-related portion of the observed motor acts.