Decreased empathy response to other people's pain in bipolar disorder: evidence from an event-related potential study

Bipolar disorder (BD) patients often demonstrate poor socialization that may stem from a lower capacity for empathy. We examined the associated neurophysiological abnormalities by comparing event-related potentials (ERP) between 30 BD patients in different states and 23 healthy controls (HCs, matched for age, sex, and education) during a pain empathy task. Subjects were presented pictures depicting pain or neutral images and asked to judge whether the person shown felt pain (pain task) and to identify the affected side (laterality task) during ERP recording. Amplitude of pain-empathy related P3 (450-550 ms) of patients versus HCs was reduced in painful but not neutral conditions in occipital areas [(mean (95% confidence interval), BD vs. HCs: 4.260 (2.927, 5.594) vs. 6.396 (4.868, 7.924)] only in pain task. Similarly, P3 (550-650 ms) was reduced in central areas [4.305 (3.029, 5.581) vs. 6.611 (5.149, 8.073)]. Current source density in anterior cingulate cortex differed between pain-depicting and neutral conditions in HCs but not patients. Manic severity was negatively correlated with P3 difference waves (pain - neutral) in frontal and central areas (Pearson r = -0.497, P = 0.005; r = -0.377, P = 0.040). Electrophysiological correlates of empathy processing are reduced in BD depending on manic symptom severity.