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Introduction

DEPRESSION, BIPOLAR DISORDER, AND ANXIETY DISORDERS have been well documented in medical writings since ancient times. In the fifth century BC, Hippocrates taught that moods depended on the balance of four humors—blood, phlegm, yellow bile, and black bile. An excess of black bile (melancholia is the ancient Greek term for black bile) was believed to cause a state dominated by fear and despondency. Robert Burton’s Anatomy of Melancholy (1621) was not only an important medical text but also viewed literature and the arts through the lens of melancholia. Such texts describe symptoms that remain familiar today; they also recognized that symptoms of depression and of anxiety often occur together.

In this chapter, we discuss mood and anxiety disorders together, not only because they frequently co-occur but also because of overlapping genetic and environmental risk factors and some shared neural structures, including regions of the amygdala, hippocampus, prefrontal cortex, and insular cortex.

Mood Disorders Can Be Divided Into Two General Classes: Unipolar Depression and Bipolar Disorder

There are no objective medical tests for mood and anxiety disorders. Thus, diagnosis depends on observation of symptoms, behavior, cognition, functional impairments, and natural history (including age of onset, course, and outcome). Patterns of familial transmission and response to treatment can also inform diagnostic classification. Based on such factors, it is possible to distinguish between two major groupings of mood disorders: unipolar depression and bipolar disorder. Unipolar depression, when severe and pervasive, is classified as major depression or major depressive disorder. Major depression is diagnosed when people suffer from depressive episodes alone. Bipolar disorder is diagnosed when episodes of mania also occur.

The lifetime risk of major depressive disorder in the United States is approximately 19%. Within any 1-year period, 8.3% of the population suffers major depression. The prevalence of depression differs in different countries and cultures; however, in the absence of objective medical tests, such epidemiologic data are subject to diagnostic and reporting biases, and thus, it is difficult to draw comparative conclusions. The World Health Organization reports that depression is a leading cause of disability worldwide, and other studies find it to be a leading cause of economic loss from noncommunicable disease. These dire social and economic consequences occur because depression is common, often begins early in life, and interferes with cognition, energy, and motivation, which are all necessary to learn in school and to work effectively.

Bipolar disorder is less common than unipolar depression, with a prevalence of approximately 1% worldwide. Its symptoms are relatively constant across countries and cultures. The incidence of bipolar disorder is equivalent in males and females.

Major Depressive Disorder Differs Significantly From Normal Sadness

Several factors distinguish major depression from transient periods of sadness that may occur in everyday life and from the grief that often follows a personal loss. These ...

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