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  • The Most Common Disorders of Mood Are Unipolar Depression and Bipolar Disorder

    • Unipolar Depression Often Begins Early in Life

    • Bipolar Disorder Includes Episodes of Mania

    • Mood Disorders Are Common and Disabling

  • Both Genetic and Nongenetic Risk Factors Play an Important Role in Mood Disorders

  • Specific Brain Regions and Circuits Are Involved in Mood Disorders

  • Depression and Stress Are Interrelated

  • Major Depression Can Be Treated Effectively

    • Antidepressant Drugs Target Monoaminergic Neural Systems

    • Psychotherapy Is Effective in the Treatment of Major Depression

    • Electroconvulsive Therapy Is Highly Effective Against Depression

    • Bipolar Disorder Can Be Treated with Lithium and Several Drugs Initially Developed as Anticonvulsants

  • Anxiety Disorders Stem from Abnormal Regulation of Fear

    • Anxiety Disorders Have a Genetic Component

    • Animal Models of Fear May Shed Light on Human Anxiety Disorders

    • Neuro-imaging Implicates Amygdala-Based Circuits in Human Fear and Anxiety

    • Anxiety Disorders Can Be Treated Effectively with Medications and Psychotherapy

  • An Overall View

Emotions are transient responses to specific stimuli in the environment (eg, the presence of danger), the body (eg, pain), or, for humans, the mind (eg, a train of thought). When an emotional state is prolonged, it can become one's dominant emotional state over time, or mood. Mood thus may be independent of immediate personal and environmental circumstances.

Mood and anxiety disorders are the most common serious disorders of the brain. Mood disorders generally involve either depression or elation. Anxiety disorders involve abnormal regulation of a powerful emotion, fear. In both mood and anxiety disorders the core symptoms have a major emotional component and are accompanied by physiological, cognitive, and behavioral abnormalities.

We discuss disorders of mood and anxiety together because both involve negative emotional states and because they appear to involve overlapping neural circuits that include the amygdala and the anterior cingulate cortex. There also is evidence for overlapping risk factors between major depressive disorder and some anxiety disorders. Commonalities of circuitry and genetic risks, as well as the negative effects of long-term anxiety on a person's mood, may explain the observation that nearly 60% of patients with major depressive disorder also suffer from an anxiety disorder. Anxiety disorder most commonly precedes the onset of depression.

Because emotions are transient responses to stimuli that can be reproduced in the laboratory, they have proven more amenable than moods to neuro-scientific study. Objective measurement of moods is difficult, compared with the more stereotypic physiological or behavioral components of emotional responses (see Chapter 48), and experimental approaches to regulating mood have had limited success. Good animal models exist for certain emotions, such as fear and pleasure, and because many features of these states appear to be conserved in evolution, the animal models are relevant to humans (see Chapter 48).

Animal models have allowed detailed investigation of the neural circuitry, physiology, and biochemistry underlying these states. For example, studies of rodent models of instinctive (unlearned) fear and learned fear (in ...

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