Shared pain: from empathy to synaesthesia.

This paper reviews the current literature on "empathy for pain", the ability to understand pain observed in another person, in the context of a newly documented form of pain empathy "synaesthesia for pain". In synaesthesia for pain a person not only empathises with another's pain but experiences the observed or imagined pain as if it was their own. Neural mechanisms potentially involved in synaesthesia for pain include "mirror systems": neural systems active both when observing an action, or experiencing an emotion or sensation and when executing the same action, or personally experiencing the same emotion or sensation. For example, we may know that someone is in pain in part because observation activates similar neural networks as if we were experiencing that pain ourselves. We propose that synaesthesia for pain may be the result of painful and/or traumatic experiences causing disinhibition in the mirror system underlying empathy for pain. We will discuss this theory in the context of a documented group of amputees who experience synaesthesia for pain in phantom limbs.