Mood disorders are characterized by marked disturbances in emotional state, which affect thinking, physical symptoms, social relationships, and behavior. If mood is viewed as a continuum, mood disorders occur when a person experiences moods that lie at either extreme of the continuum. Mood disorders are of two basic types: unipolar or bipolar. People with unipolar disorders experience moods that are at the depressive end of the continuum. People with bipolar disorders experience moods that are at both ends of the continuum.
Mood disorders are generally episodic, which means they tend to come and go. The duration of the disturbed emotional state and the pattern of its occurrence determine how a mood disorder is diagnosed.
A person with dysthymic disorder experiences a depressed mood for a majority of days over at least two years.
Major Depressive Disorder
Major depressive disorder is characterized by at least one major depressive episode. A major depressive episode is a period of at least two weeks in which a person experiences some or all of the following symptoms:
- Constant sadness or irritability
- Loss of interest in almost all activities
- Changed sleeping or eating patterns
- Low energy
- Feelings of worthlessness or guilt
- Difficulty concentrating
- Recurrent thoughts about suicide
Major depressive disorder is much more common in women than in men.
Bipolar disorders involve at least one distinct period when a person exhibits manic symptoms. Manic symptoms include any or all of the following:
- Feelings of being high
- Decreased need for sleep
- Inflated self-esteem or grandiosity
- Fast and pressured speech
- Increased interest in pleasurable activities that have the potential for harmful consequences.
People with bipolar disorders usually also experience major depressive episodes. Men and women are equally likely to suffer from bipolar disorders.
Etiology of Mood Disorders
Researchers believe that many different influences interact to produce mood disorders.
Biological influences include the following:
- Genetic predisposition: Twin studies suggest that people can be genetically predisposed to major depressive disorder and bipolar disorders. Concordance rates for both major depressive disorder and bipolar disorders are higher for identical twins than fraternal twins. Genetic factors seem to be implicated more in depression among women than among men.
- Neurotransmitters: Research shows that the neurotransmitters norepinephrine and serotonin are involved in mood disorders.
- Brain structure: Some research indicates that people with chronic depression tend to have a smaller hippocampus and amygdala in the brain, perhaps because of an excess of the stress hormone cortisol.
Many researchers have studied the various cognitive factors involved in depression:
- Learned helplessness: The psychologist Martin Seligman proposed that depression results from learned helplessness, or a tendency to give up passively in the face of unavoidable stressors. Seligman pointed out that people who have a pessimistic explanatory style are likely to experience depression.
- Self-blame: Depressed people tend to attribute negative events to internal, stable, and global factors. When a problem occurs, they blame themselves rather than situational factors. They believe the problem is likely to be permanent, and they overgeneralize from the problem to their whole lives.
- Low self-esteem: Some researchers have suggested that a pessimistic worldview is only one of several factors that contribute to depression. They say that other factors such as low self-esteem and stress also play an important role. All these lead to hopelessness, which then leads to depression.
- Rumination: Rumination, or brooding about problems, is associated with longer periods of depression. Some researchers believe that women have higher rates of depression because they tend to ruminate more than men.
Although many researchers believe negative thinking makes people susceptible to depression, most also acknowledge a two-way relationship between depression and negative thinking. Negative thinking makes people susceptible to depression, and depression makes people more likely to think negatively.
Various interpersonal influences are also linked to depression:
- Lack of social network: Depressed people tend to have less social support than other people, and the relationship between social support and depression is likely to be two-way. People with poor social skills may be more likely to develop depression. Once people are depressed, they tend to be unpleasant companions, which further reduces their social support.
- Loss of an important relationship: Some researchers have suggested that depression can result when people lose important relationships.
The onset and course of mood disorders may be influenced by stress. Stress also affects people’s responses to treatment and whether they are likely to have a relapse. Some researchers have suggested that women are more vulnerable to depression because they tend to experience more stress in the form of discrimination, poverty, and sexual abuse and because they may have less satisfying work and family lives than men.
Even if people are usually happy and have friends and family to rely on, they can still become depressed. Major catastrophes and personal traumas can also contribute to depression. For instance, living in a war zone, having a home destroyed by fire, suffering from a chronically painful or debilitating illness, going through a divorce, or losing a loved one can all bring on depression.