Empathy for Pain in the human Somatosensory System: a Somatosensory Evoked Potentials Study

Current neuroscientific models of empathy postulate that a given motor, perceptual or emotional state of an individual activates corresponding representations and neural processes in another individual who observes that state. Pain is a complex feeling with at least two major sensory-discriminative (e.g. intensity, duration of the noxious stimulus) and affective-motivational (e.g. unpleasantness) components that are mapped in separate nodes of a cortico-subcortical neural network referred to as the ‘pain matrix’. The sensory dimension of pain is mainly coded in sensorimotor neural structures, while the affective component is mainly mapped in cingulate and insular cortices. Recent fMRI studies suggest that only the affective component of the pain matrix is crucial for the empathic matching of others’ pain. Here we investigated the somatosensory side of empathy for pain by recording somatosensory evoked potentials (SEPs) during observation of ‘flesh and bone’ painful and non-painful stimuli delivered on the body of a human model. Subjects were presented with video-clips depicting: i) a needle penetrating a dorsal view of a male right hand (pain); ii) a Q-Tip moving over and pressing the same region of the hand (touch); a static dorsal view of the same right hand (static hand); iv) a fixation point. After the SEPs recording session, subjects were asked to rate along a 0-10 VAS, the Intensity and Unpleasantness of the sensation purportedly experienced by the model and Arousal and Aversion (personal distress) induced by each movie. For each component, peak voltage amplitude values in each hand observation block were normalized with respect to the fixation block and entered into repeated measure one-way ANOVAs with observation condition as main factor (three levels: pain, touch, static hand). A significant main effect was found for peak amplitude values of the P40 component, which is likely to be generated by neural activity in the primary somatic cortex. Post-hoc analysis showed that P40 amplitudes resulted significantly higher in PAIN condition than in HAND and TOUCH conditions. Furthermore, this effect was significantly predicted by the sensory (Intensity) but not by the affective (Unpleasantness) qualities of the pain ascribed to the model or by measures of self-related emotional reactions (Aversion, Arousal). Results suggest that the modulation of SI activity contingent upon observation of others’ pain may reflect a mapping of sensory qualities of observed pain