Mood disorders are known to be at least in part genetic, because they are heritable. (Berrettini, 2006; Merikangas et al., 2002). 1 Neurotransmitters also play an important role in mood disorders. Serotonin, dopamine, and norepinephrine are all known to influence mood (Sher & Mann, 2003), 2 and drugs that influence the actions of these chemicals are often used to treat mood disorders.
The brains of those with mood disorders may in some cases show structural differences from those without them. Videbech and Ravnkilde (2004) 3 found that the hippocampus was smaller in depressed subjects than in normal subjects, and this may be the result of reduced neurogenesis (the process of generating new neurons) in depressed people (Warner- Schmidt & Duman, 2006). 4Antidepressant drugs may alleviate depression in part by increasing neurogenesis (Duman & Monteggia, 2006). 5
Research Focus: Using Molecular Genetics to Unravel the Causes of Depression
Avshalom Caspi and his colleagues (Caspi et al., 2003) 6 used a longitudinal study to test whether genetic predispositions might lead some people, but not others, to suffer from depression as a result of environmental stress. Their research focused on a particular gene, the 5-HTT gene, which is known to be important in the production and use of the neurotransmitter serotonin. The researchers focused on this gene because serotonin is known to be important in depression, and because selective serotonin reuptake inhibitors (SSRIs) have been shown to be effective in treating depression.
People who experience stressful life events, for instance involving threat, loss, humiliation, or defeat, are likely to experience depression. But biological-situational models suggest that a person’s sensitivity to stressful events depends on his o r her genetic makeup. The researchers therefore expected that people with one type of genetic pattern would show depression following stress to a greater extent than people with a different type of genetic pattern. The research included a sample of 1,037 adults from Dunedin, New Zealand. Genetic analysis on the basis of DNA samples allowed the researchers to divide the sample into two groups on the basis of the characteristics of their 5- HTT gene. One group had a short version (orallele) of the gene, whereas the other group did not have the short allele of the gene.
The participants also completed a measure where they indicated the number and severity of stressful life events that they had experienced over the past 5 years. The events included employment, financial, housing, health, and relationship stressors. The dependent measure in the study was the level of depression reported by the participant, as assessed using a structured interview test (Robins, Cottler, Bucholtz, & Compton, 1995). 7
As you can see in Figure 12.4,
as the number of stressful experiences the participants reported increased from 0 to 4, depression also significantly increased for the participants with the short version of the gene (top
panel). But for the participants who did not have a short allele, increasing stress did not increase depression (bottom panel). Furthermore, for the participants who experienced 4 stressors
over the past 5 years, 33% of the participants who carried the short version of the gene became depressed, whereas only 17% of participants who did not have the short version did.
This important study provides an excellent example of how genes and environment work together: An individual’s response to environmental stress was influenced by his or her genetic makeup.
But psychological and social determinants are also important in creating mood disorders and depression. In terms of psychological characteristics, mood states are influenced in large part by our cognitions. Negative thoughts about ourselves and our relationships to others create negative moods, and a goal of cognitive therapy for mood disorders is to attempt to change people’s cognitions to be more positive. Negative moods also create negative behaviors toward others, such as acting sad, slouching, and avoiding others, which may lead those others to respond negatively to the person, for instance by isolating that person, which then creates even more depression (Figure 12.5). You can see how it might become difficult for people to break out of this “cycle of depression.”
Weissman et al. (1996) 8 found that rates of depression varied greatly among countries, with the highest rates in European and American countries and the lowest rates in Asian countries. These differences seem to be due to discrepancies between individual feelings and cultural expectations about what one should feel. People from European and American cultures report that it is important to experience emotions such as happiness and excitement, whereas the Chinese report that it is more important to be stable a nd calm. Because Americans may feel that they are not happy or excited but that they are supposed to be, this may increase their depression (Tsai, Knutson, & Fung, 2006). 9
- Mood is the positive or negative feelings that are in the background of our everyday experiences.
- We all may get depressed in our daily lives, but people who suffer from mood disorders tend to experience more intense—and particularly more intense negative—moods.
- The most common symptom of mood disorders is negative mood.
- If a person experiences mild but long-lasting depression, she will be diagnosed with dysthymia. If the depression continues and becomes even more severe, the diagnosis may become that of major depressive disorder.
- Bipolar disorder is characterized by swings in mood from overly “high” to sad and hopeless, and back again, with periods of near-normal mood in between.
- Mood disorders are caused by the interplay among biological, psychological, and social variables.
EXERCISES AND CRITICAL THINKING
- Give a specific example of the negative cognitions, behaviors, and responses of others that might contribute to a cycle of depression like that shown inFigure 12.13 "Cycle of Depression".
- Given the discussion about the causes of negative moods and depression, what might people do to try to feel better on days that they are experiencing negative moods?