A study of the observation of pain by spinal cord injured people reveals the topographic mapping of the sensorimotor qualities of empathic reactivity.

The experience of empathy for pain is underpinned by sensorimotor and affective dimensions which are behaviourally and neurally distinct. Spinal cord injuries (SCI) induce a massive, below-lesion level, sensorimotor body-brain disconnection. This condition may make it possible to test whether sensorimotor deprivation alters specific dimensions of empathic reactivity to observed pain. To explore this issue, we asked SCI people with paraplegia and healthy controls to observe videos of painful or neutral stimuli administered to a hand (intact) or a foot (deafferented). The stimuli were displayed by means of a virtual reality set-up and seen from a first person (1PP) or third person (3PP) visual perspective. A number of measures were recorded: behaviour measures (from explicit verbal reports on the videos) and implicit measures of muscular activity (from an EMG from the corrugator and zygomatic muscles) representing a proxy of sensorimotor dimensions and of autonomic reactivity (the electrodermal response and Respiratory Sinus Arrhythmia) representing a proxy of affective dimensions. While no across group differences in the explicit verbal reports on the stimuli depicting pain were found, the SCI people exhibited reduced facial muscle reactivity for the stimuli applied to the foot (but not the hand) seen from the 1PP. Tellingly, the corrugator activity (an index of sensorimotor empathic reactivity) correlated with SCI participants’ neuropathic pain. There were no across group differences in autonomic reactivity suggesting that SCI lesions may affect sensorimotor more than the affective dimensions connected to empathy for pain.