Abnormality of Reward Sensitivity in Major Depressive Disorder and Bipolar Disorder

Abstract

Bipolar disorder (BD) and major depressive disorder (MDD) are two major psychiatric disorders that both involve a reward system abnormality. This paper reviews studies on the hyper/hyposensitivity model, also known as the Behavior Approach System (BAS), that emphasize the role of abnormal reward processing in patients with BD and MDD. The paper concludes that BD patients' extremely high reward sensitivity causes manic-related symptoms as well as bipolar depressive symptoms. On the contrary, MDD patients' extremely low reward sensitivity leads to unipolar depressive symptoms such as anhedonia and loss of motivation. Furthermore, this paper discusses the hyper/hyposensitivity model's utility in three areas: how it can aid in disease differentiation and prediction, and how it can be used to develop potential treatments. Because reward sensitivity can be measured using reward tasks, predicting the onset of BD and MDD, making the correct diagnosis, and developing treatments will be easier if the relationship between sensitivity and diseases is clear.