Reward Hypersensitivity in Bipolar Spectrum Disorders

The behavioral approach system (BAS)/reward hypersensitivity model of bipolar disorder proposes that risk for bipolar disorder, in particular hypo/manic episodes, is characterized by a hypersensitivity to goal- and reward-relevant cues. This hypersensitivity can lead to an excessive increase in approach-related affect and motivation to positive or rewarding life events, which, in the extreme, is reflected in hypo/manic symptoms. By contrast, multiple other psychiatric disorders, including major depressive disorder, attention deficit hyperactivity disorder, schizophrenia, and anxiety, appear to be characterized by reduced or unaffected reward processing. This suggests that elevated reward processing may be unique to bipolar disorder and thus important for understanding the differential risk for bipolar symptoms and the pathophysiology of hypo/manic episodes. The objective of the present chapter is four-fold. First, the literature on reward processing and reward-related neural activation in bipolar disorder is reviewed, in particular risk for hypomania/mania. Second, it is proposed that reward-related neural activation reflects a unique biological marker of risk for bipolar disorder that may help facilitate psychiatric assessment and differential diagnosis. Third, the pharmacological and psychosocial treatment implications of research on reward-processing and reward-related neural activation in bipolar disorder are addressed. Finally, new and novel directions of research on reward processing in bipolar disorder are discussed, including an integrated reward and circadian rhythm dysregulation model of bipolar symptoms and our neuroimmune network hypothesis of abnormalities in reward processing across mood-related disorders.