Mirror-touch synaesthesia in the phantom limbs of amputees.

In mirror-touch synaesthesia merely observing another person being touched will cause the observers to experience a touch sensation on their own body. The current study investigates whether this, normally a developmental condition, might be acquired following amputation. Twenty-eight amputees observed 67 videos of touch events and indicated a) whether the video elicited tactile sensations, b) where on the body this was located, c) the intensity of the sensation, and d) whether it was painful. Almost a third of amputees report a tactile sensation on their amputated phantom limb when watching someone else being touched. In this particular group the sensations tend to be localised on the phantom limb or stump, but are rarely reported elsewhere on the body. This occurs irrespective of the body part seen. The synaesthetic sensations were more intense when real bodies were observed relative to dummies or objects, and when the observed touch is mildly painful relative to non-painful. Although frequency, intensity and cause of phantom limb pain do not appear to determine whether an amputee will report mirror-touch sensations, those who do report it show greater empathic emotional reactivity. These results suggest that acquired synaesthesia may be linked with sensory loss, arising after amputation, and that highly empathic individuals could be predisposed to strengthening existing pathways between observed touch and felt touch.