Every day, we do things that cause effects in the outside world with little doubt about who caused what. To some, this sense of agency derives from a post hoc reconstruction of a likely causal relationship between an event and our preceding movements; others propose that the sense of agency originates from prospective comparisons of motor programs and their effects. Using functional magnetic resonance imaging, we found that the sense of agency is associated with a brain network including the pre–supplementary motor area (SMA) and dorsal parietal cortex. Transcranial magnetic stimulation affected the sense of agency only when delivered over the pre-SMA and specifically when time-locked to action planning, rather than when the physical consequences of the actions appeared. These findings make a prospective theory of the sense of agency more likely.

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Background: Associative plasticity, the neurophysiological bases of Hebbian learning, has been implied in the formation of the association between sensory and motor representations of actions in the Mirror Neuron System; however, such inductor role still needs empirical support. Objective/hypothesis: We have assessed whether Paired Associative Stimulation (PAS), known to activate Hebbian associative plasticity, can induce the formation of atypical (absent in normal conditions), visuomotor associations, reshaping motor resonance. Methods: Healthy participants underwent a novel PAS protocol (mirror-PAS, m-PAS), during which they were exposed to repeated pairings of transcranial magnetic stimulation (TMS) applied over the right primary motor cortex (M1), time-locked with the view of index-finger movements of the right (ipsilateral) hand. In a first experiment, the inter-stimulus interval (ISI) between visual-action stimuli and TMS pulses was varied. Before and after each m-PAS session, motor resonance was assessed by recording Motor Evoked Potentials induced by single-pulse TMS applied to the right M1, during the observation of both contralateral (left) and ipsilateral (right) index-finger movements. In the second experiment, the specificity of the m-PAS was assessed by presenting a visual stimulus depicting a non-biological movement.Results: Before m-PAS, the facilitation of corticospinal excitability occurred only during the view of contralateral (with respect to the TMS side) index-finger movements. The m-PAS induced new ipsilateral motor resonance responses, indexed by atypical facilitation of corticospinal excitability by the view of ipsilateral hand movements. This effect occurred only if the associative stimulation followed the chronometry of motor control (ISI of 25 ms) and if the visual stimulus of the m-PAS depicts a biological movement (human hand action). Conclusions: The present findings provide the first empirical evidence that Hebbian learning induced by a PAS protocol shapes the visual-motor matching properties of the human Mirror Neuron System.