Freezing or escaping? Opposite modulations of empathic reactivity to the pain of others.

Perceiving pain in others may induce the covert simulation of both sensory and emotional components of others' pain experience. Previous transcranial magnetic stimulation (TMS) studies have investigated the motor counterpart of this resonant mapping by showing suppression of motor-evoked potentials (MEPs) during the observation of a needle entering body parts of another person. Here we explored whether MEPs recorded from an onlooker's hand (e.g., the right hand, TMS to the left motor cortex) are differentially influenced by the observation of painfully stimuli delivered to the same (right) or the opposite (left) hand in a model. Congruency between observed (model) and recorded (onlooker) hand brought about a reduction of MEPs amplitude. This resonant inhibitory response in the onlooker was specific for the muscle penetrated in the model. In contrast, observing pain on the model's hand opposite to that from which MEPs were recorded brought about a generalized increase of hand corticospinal excitability. Corticospinal inhibition and facilitation effects were comparable in the two hemispheres and specific for the corresponding and opposite hand. Results suggest that observing pain in another person's hand automatically induces the covert simulation of potentially adaptive freezing and avoidance responses in the onlooker's corticospinal system.