Reduced empathic pain processing in patients with somatoform pain disorder: Evidence from behavioral and neurophysiological measures

The present study aimed to investigate the alterations of psychophysiological responses to empathy for pain among patients with somatoform pain disorder (SPD). Behavioral and event-related potential (ERP) responses to pictures depicting hands or feet in different non-painful or painful situations were compared between 18 SPD patients and 18 healthy controls. Patients with SPD reported lower unpleasantness to the observation of others' pain than healthy controls, thus suggesting a reduced affective sharing to others' pain in SPD. While healthy controls showed significant different N2 and P3 responses between painful and non-painful stimulations, no significant difference was observed for patients with SPD. In addition, while both patients and controls showed enlarged late positive potential (LPP) response to painful stimulation than to non-painful stimulation, the differential LPP response was significantly smaller in patients than controls. These ERP results suggested a reduced response to empathy for pain in both early affective and late cognitive temporal stages in SPD. Mediation analysis further revealed that alexithymia mediated the effect of somatoform pain on empathic N2 responses, suggesting that the reduced early affective sharing process in SPD was mediated by their heightened alexithymia. To sum up, our results demonstrated the reduced psychophysiological responses to empathy for pain among patients with SPD, where the reduced affective sharing process could be explained by the concurrent alexithymia. While the altered empathy for pain exhibited by these patients with SPD could impact their social functioning, our study would provide some insights into interventions aimed at improving empathy-related social functioning.