Introduction: Psychological pain is a frequently observed symptom in depression, and escape from unbearable psychological pain is often mentioned as the reason for suicide. We explored the relationship between psychological pain and two potential biomarkers: heart rate variability (HRV) and frontal EEG alpha-asymmetry. As both markers have successfully been used as feedback to alter mood state, knowledge about the relationship between HRV, frontal EEG, and psychological pain may be of particular interest for interventions to alleviate psychological pain.
Methods: Adults with a history of depression (N = 35) participated in six 5-minute sessions during which heart rate and EEG were recorded, while the participants sat upright with their eyes closed. In addition, participants completed the Beck scales for depression, hopelessness, and suicide ideation, and two measures of psychological pain: the Psychache Scale and the Orbach & Mikulincer Mental Pain (OMMP) Questionnaire.
Results: Mean age of the participants was 35.0 (SD 11.84) and their average level of depression and hopelessness was moderate. The intraclass correlation coefficient indicated excellent agreement of neurophysiological variables across successive measurements. In separate hierarchical regression models, after controlling for depression and hopelessness, low-frequency HRV and right midfrontal delta power contributed significant variance (delta R2 = 8.8%, beta = -.30, p = .02 and delta R2 = 7.0%, beta = -.26, p = .03, respectively) to the prediction of current psychological pain on the OMMP. For worst-ever psychological pain on the OMMP, midfrontal delta power contributed significant variance (delta R2 = 20.5%, beta = -.45, p = .004), after controlling for depression. Suicidal desire moderated the relationships of low-frequency HRV and midfrontal delta power to psychological pain on the Psychache Scale. High-frequency HRV and frontal alpha-asymmetry did not correlate with the Psychache Scale or OMMP scores. EEG asymmetry based on fractal dimensions decreased (greater left than right complexity) with increasing current and worst-ever psychological pain on the OMMP.
Conclusion: Findings suggest that greater psychological pain is associated with increased sympathetic nervous system activity, rather than with reduced parasympathetic nervous system activity. Psychological pain may affect the right frontal cortex more adversely than the left frontal cortex.