A comparative study of theory of mind, psychological flexibility, and executive functions in patients with unipolar and bipolar depression during remission and matched healthy controls

Objective: This study aimed to compare patients with unipolar and bipolar depression during remission in terms of executive functions, theory of mind, emotion and face recognition, and psychological flexibility, and to examine which of these factors are most closely related to each other. Materials and Methods: The study included 40 patients with unipolar depression, 42 patients with bipolar depression (both in remission), and 45 healthy control participants matched for age, gender, and educational background. Participants were first administered a sociodemographic and clinical data form, followed by the Beck Depression and Anxiety Inventories, Acceptance and Action Questionnaire-II, Psychological Flexibility Questionnaire, and the Freiburg Mindfulness Inventory. Subsequently, all participants completed the Benton Facial Recognition Test, the Dokuz Eylül Theory of Mind Scale, the Ekman Facial Expressions Recognition Test, the Wisconsin Card Sorting Test (WCST), and the Stroop Test. Results: There were no significant differences between the groups in terms of age, gender, years of education, or socioeconomic status. However, the proportion of single individuals was higher in both patient groups compared to the control group. Additionally, the bipolar group had significantly lower rates of having children, employment, and comorbid psychiatric conditions. Bipolar patients had an earlier age of illness onset and differed significantly from the other groups in variables such as electroconvulsive therapy (ECT) history, psychotherapy, psychiatric hospitalization, psychotic symptoms, seasonality, episode severity, and number of episodes. Depression and anxiety scores were higher in both patient groups, while psychological flexibility, mindfulness, social cognition, and facial recognition scores were significantly lower compared to healthy controls. Executive function impairments—particularly in the bipolar group—were evident in the WCST and Stroop Test results. In emotion recognition tasks, both patient groups performed poorly in recognizing negative emotions such as fear, disgust, and anger. Conclusion: This study compared the performance of remitted unipolar and bipolar depression patients with healthy individuals in the domains of theory of mind, emotion and face recognition, executive functions, and psychological flexibility. The findings indicated that both patient groups exhibited marked impairments across all domains compared to healthy controls, and these impairments persisted even during remission. Although theory of mind and emotion recognition abilities appeared to be more affected in the bipolar group in some subdomains, distinct differences between the two patient groups were limited. Executive dysfunctions, particularly in cognitive flexibility and attentional control, were prominent. Both patient groups demonstrated significantly lower levels of psychological flexibility, which was also associated with social cognition and executive functioning. Correlation analyses revealed significant relationships among some variables—particularly between face recognition, social cognition, and executive functions. Overall, the findings suggest that depression is not merely a mood disorder, but a multidimensional condition involving impairments in both social and cognitive functioning. Therefore, treatment approaches should address not only symptomatology but also cognitive and social-cognitive domains. Keywords: Unipolar depression, bipolar depression, social cognition, theory of mind, emotion-face recognition, psychological flexibility, executive functions