Study Of Pain Empathy In Patients With Bipolar Disorder Using Event-related Potential Methods

Objective: Bipolar disorder is a kind of disease featured by both manic or hypomanic and depressive episodes. It has been demonstrated that patients with bipolar disorder showed impairment in social cognition in domains including emotion processing, theory of mind, empathy and so on. Empathy refers to the ability to recognize and share the emotional states of others, which is crucial to social interaction. There have been little researches investigating the ability of empathy in the patients with bipolar disorder. Moreover, the only existed researches indicated patients with bipolar disorder had poorer empathy compared to healthy controls in behavioral levels, while the neural mechanism was not clear so far. In the present study, we aimed to use event-related potential(ERP) methods with high temporal resolution to investigate neural mechanism underlying empathy in patients with bipolar disorder by the use of well-developed pain empathy paradigm.Methods:(1) Subjects: Thirty patients diagnosed with bipolar disorder and 25 healthy controls were involved in the study. All patients were diagnosed with bipolar disorder referring to the diagnostic criteria of bipolar disorder in 10 th version of International Classification of Diseases(ICD-10). They were stable or remitted with no psychiatric symptom and no history of electroconvulsive shock in the last 6 months and all taking medicine. Healthy controls without any psychosis or history of known family member with psychosis were included and they were matched to patients in age, gender and education. Subjects with severe somatopathy or impaired vision or those who were unable to complete the tasks independently were excluded.(2) Empathy questionnaire: All subjects completed the Chinese version of Interpersonal Reactivity Index.(3) Pain empathy paradigm: Referring to previous study, 140 painful and neural pictures were taken and involved in the tasks. Subjects were demanded to judge whether the person in the pictures felt painful(pain judgment) or the laterality of the body parts(hands or feet) of that person(laterality judgment) and EEG were recorded in the meanwhile. After EEG recording, subjects were asked to rate the degree of pain according to the person in pictures.Results:(1) Behavioral results: patients showed lower scores in empathy concern subscale and longer react time in all conditions.(2) Electrophysiological results: N1(105-155ms) amplitudes in healthy controls induced by painful stimuli were larger than those by neutral stimuli in pain judgment, and the difference was not found in laterality judgment. However, the difference of amplitudes of N1 between painful and neutral stimuli disappeared in pain judgment as well as in laterality judgment in BD patients. P3(450-550 ms and 550-650ms) amplitudes induced by painful stimuli in healthy controls were larger than those by neutral stimuli in pain judgment, and the difference was not found in laterality judgment. BD patients showed the same pattern but amplitudes induced by painful stimuli were smaller in patients compared to healthy controls in pain judgment.(3) Source-Localization Data: current source density of the brain regions involved in pain judgment were larger than that in neural condition in painful condition in healthy controls, but it was similar in BD patients.Conclusion: Both decreased early and late amplitudes induced by painful stimuli compared to neutral stimuli were found in BD patients, and the activation of ACC related to pain empathy processing was decreased in patients. The ability of pain empathy was impaired in patients with bipolar disorder.