There is a long-standing debate about whether bipolar disorder and schizophrenia should be considered separate diseases or different manifestations of the same pathophysiological process. For example, genetic studies have shown shared risk genes (but not copy number variants) for bipolar disorder and schizophrenia (1
). In contrast, while individuals with both disorders exhibit difficulties in community functioning, the clinical presentations are partially distinct in that patients with bipolar disorder tend to show better social connectedness when not in a mood episode relative to schizophrenia patients (3
). Cognition is a strong determinant of functioning in both disorders (4
); however, the magnitude of impairment in different domains of cognition across disorders is not well understood.
Most of our knowledge of cognitive deficits in both bipolar disorder and schizophrenia comes from studies of nonsocial cognition (e.g., attention, memory) (5
). However, the degree of impairment in social cognition relative to nonsocial cognition is not well established in either disorder, and social cognition has not been systematically examined in bipolar disorder across subdomains. Social cognition refers to the ability to recognize, reason about, and appropriately respond to socioemotional information, such as the emotions, intentions, and dispositions of others (7
). Social cognition can be divided into low-level processes that involve recognition and perception of socioemotional cues, including facial expression, vocal intonation, and gestures, and high-level processes that include inferences about the mental states of others (i.e., mental state attribution), empathy, and emotional regulation (7
The literature on social cognition in schizophrenia has grown rapidly in the past decade. Schizophrenia patients exhibit impairments in both low- and high-level social cognitive processes (8
), and their impaired social cognition is consistently related to functional outcome (12
). Much less is known about social cognition in bipolar disorder, and the few studies on this topic have been largely limited to facial affect recognition and mental state attribution. Studies of facial affect perception have shown inconsistent findings in the disorder, with some studies finding intact facial affect perception and others finding impairments in bipolar patients relative to comparison subjects (14
). Most studies have included relatively small patient samples with varied clinical symptoms (e.g., depressed or manic mood episode). For mental state attribution, bipolar patients in a mood episode have shown impairment (17
). Although findings in remitted patients are mixed (19
), a meta-analytic study found moderately impaired mental state attribution in remitted bipolar patients (21
). Thus, it remains unclear whether social cognitive impairments exist outside of mood episodes or whether these impairments would be observed across a variety of social cognitive tasks. Furthermore, neither the level nor the pattern of social cognitive performance has been directly compared across bipolar disorder and schizophrenia.
In this study, we aimed to directly compare the level and pattern of social and nonsocial cognitive performance in bipolar disorder and schizophrenia patients using behavioral tasks. First, we evaluated the performance of patients with bipolar disorder on each social cognitive task separately (emotion perception, emotion regulation, empathic accuracy, mental state attribution, and self-referential memory). Although most of the tasks have been validated in healthy adults and have been used in studies of schizophrenia patients, they have not previously been used in studies of bipolar disorder. We also explored whether subgroups of bipolar disorder patients (defined by clinical features or medication status) would perform differently on social and nonsocial cognitive tasks. Second, we examined whether bipolar disorder and schizophrenia patients would show similar patterns of performance (i.e., profiles) across social and nonsocial cognitive tasks. Third, we compared the level of impairment on social and nonsocial cognitive domains across the two disorders.