Role of sensorimotor areas in early detection of motor errors: An EEG and TMS study.

Action execution is prone to errors and, while engaged in interaction, our brain is tuned to detect deviations from what one expects from other's action. Prior research has shown that Event-Related-Potentials (ERPs) are specifically modulated by the observation of action mistakes interfering with goal achievement. However, in complex and modular actions, embedded motor errors do not necessarily produce an immediate effect on the global goal. Here we dissociate embedded motor goals from global action goals by asking subjects to observe familiar but untrained knotting actions. During knotting an embedded motor error (i.e. the rope is inserted top-down instead of bottom-up during the formation of a loop) while not producing any immediate mistake, may strongly affect the final result. We found that embedded errors elicit in the observer specific early fronto-central negativity (120-180 ms). In a second experiment, we online administered exicitatory transcranial magnetic stimulation (TMS) over central (C3) or occipital (Oz) scalp locations, at the timing of the ERP components observed in the first experiment. C3 stimulation produced a significant improvement in embedded error discrimination performance. These results show that sensorimotor areas are instrumental in the early detection of embedded motor errors. We conclude that others' embedded errors provide fundamental cues which, inserted within a complex hierarchical action plan, might be used by the observer to anticipate whether an action will eventually fail