Effects of being imitated on motor responses evoked by pain observation: exerting control determines action tendencies when perceiving pain in others.

Brain-imaging research has shown that experiencing pain oneself and perceiving pain in others lead to a similar pattern of activation, suggesting that the latter is based on internal simulation of the observed pain. Further evidence for this idea stems from transcranial magnetic stimulation measuring corticospinal excitability (CSE). It has been demonstrated that our motor cortex is involved whenever we observe another person receiving painful stimulation to the hand (Avenanti et al., 2005). However, both decreases and increases of CSE have been described during pain observation, so the exact nature of these CSE changes has remained unclear so far. In the present study, we hypothesized that CSE changes are determined by the control that the observer has over the hand that receives painful stimulation. To test this hypothesis, we manipulated the control over the observed hand using a paradigm in which participants' movements are being imitated by a hand on screen-giving them full control over the hand-or not. Consistent with previous results, we evidenced a decrease in CSE when participants experienced no control over the hand that received painful stimulation. In contrast, inducing control resulted in an increase in CSE. We conclude that exerting control over the observed hand leads to a completely altered action tendency. Whereas an anesthetic response is typically observed in the absence of control, increasing control induces motor facilitation reminiscent of preparation of an avoidance response