Differentiating bipolar I disorder, bipolar II disorder and unipolar depression based on neurobiological alterations of Grays behavioral activation and inhibition system (BAS/BIS)

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Bipolar disorder is a devastating mental disease characterized by recurrent episodes of depressed and elevated mood. As our knowledge concerning the etiology of bipolar spectrum disorders is rather limited, diagnosis is based on behavioral manifestations. This has the side effect that at onset bipolar spectrum disorders and in particular bipolar II disorder are often misdiagnosed as unipolar depression leading to detrimental effects on the course of the disease. Interestingly, both bipolar and unipolar affective disorders might be seen as disorders of aberrant motivation herein referring to the process of initiating, controlling and maintaining behavior with the goal of maximizing pleasurable outcomes. During depression a diminished interest in almost all activities is observed, whereas during mania patients display excessive involvement in pleasurable activities with a high probability of negative long-term consequences. It is assumed that reduced (depression) / increased (mania) approach motivation towards appetitive stimuli as well as increased (depression) / reduced (mania) processing of aversive stimuli, is related to alterations in the behavioral activation system (BAS). Further, alterations in the behavioral inhibition system (BIS) that regulates the BAS in case of approach-avoidance conflicts might also be of relevance in mood disorders. First evidence also suggests that rumination referring to repeated, often realistic thoughts concerning one topic mediates the association between increased BAS-sensitivity and manic symptoms. However, BAS, BIS and rumination as well as their neurobiological correlates have not been systematically studied in patients with affective disorders. The proposed study likes to investigate three patient groups: bipolar I disorder, bipolar II disorder and unipolar depression with regard to approach and avoidance behavior and rumination. Applying magnetic resonance imaging (MRI), we like to identify functional biomarkers that allow differentiation of these disorders with sufficient sensitivity and specificity. Participants would undergo extensive clinical diagnostics, neuropsychological testing, an approach-avoidance task and a rumination task during MRI. Data will be analyzed in the context of the general linear model and with machine learning algorithms.