Parieto-frontal mechanisms underlying observation of complex hand-object manipulation

The observation of actions performed by others is believed to activate the Action Observation Network (AON). Previous evidence suggests that subjects with a specific motor skill show increased activation of the AON during observation of the same skill. The question arises regarding which modulation of the AON occurs during observation of novel complex manipulative actions that are beyond the personal motor repertoire. To address this issue, we carried out a functional MRI study in which healthy volunteers without specific hand motor skills observed videos displaying hand-object manipulation executed by an expert with high manual dexterity, by an actor with intermediate ability or by a naive subject. The results showed that the observation of actions performed by a naive model produced stronger activation in a dorso-medial parieto-premotor circuit including the superior parietal lobule and dorsal premotor cortex, compared to observation of an expert actor. Functional connectivity analysis comparing the observation of the naive model with that of the expert model, revealed increased connectivity between dorsal areas of the AON. This suggests a possible distinction between ventral and dorsal brain circuits involved in the processing of different aspects of action perception, such as kinematics and final action goal.