When we watch someone else being pricked by a needle in their hand, the corticospinal motor neurons connected to that specific part of our own hand are inhibited, just as they would be if we’d been injected ourselves. It’s as though our brain has specifically identified where the other person has been hurt and mapped this information onto our own mental body map. The finding adds to an emerging picture that suggests we empathise with other people’s pain by simulating their suffering in our own central nervous system.
Alessio Avenanti and his team applied transcranial magnetic stimulation (TMS) to their participants’ heads, over the motor cortex, and observed how much electrical activity this triggered in the participants’ hand muscles. The amount of activity the TMS triggered in a participant’s hand muscle was reduced when they watched a video of someone being injected in that same hand region, but not when they watched a foot injection, a tomato being injected or a non-painful cue tip being used instead.
“We suggest the effect may be due to activation of a pain resonance system that extracts basic sensory aspects of the model’s (i.e. other person’s) painful experience and maps them onto the observer’s motor system according to topographic rules”, the researchers said.
Pain is thought to be closely linked to our brain’s action systems so that we can freeze suddenly or flee quickly – whichever is better for our survival. Now this study has shown that other people’s pain also affects our brain’s action systems. “Philosophers have emphasised that our bodily sensations are intrinsically private”, the researchers concluded. “However, our findings suggest that, at least in humans, the social dimension of pain extends even to the very basic, sensorimotor levels of neural processing”.
Avenanti, A., Bueti, D., Galati, G. & Aglioti, S.M. (2005). Transcranial magnetic stimulation highlights the sensorimotor side of empathy for pain. Nature Neuroscience, 8, 955-960.