Mood disorders result from a combination of risk factors although researchers do not yet know exactly how these elements interact to cause a mood disorder (Moffitt, Caspi, & Rutter, 2006).
Biological Factors Genetic factors can play an important role in the development of depression (Haghighi et al., 2008; Zubenko et al., 2003) and bipolar disorder (Badner, 2003; Serretti & Mandelli, 2008). Strong evidence comes from studies of twins. (See Chapter 2, “The Biological Basis of Behavior.”) If one identical twin is clinically depressed, the other twin (with identical genes) is likely to become clinically depressed also. Among fraternal twins (who share only about half their genes), if one twin is clinically depressed, the risk for the second twin is much lower (McGuffin, Katz, Watkins, & Rutherford, 1996). In addition, genetic researchers have recently identified a specific variation on the 22 chro- mosome that appears to increase an individual’s susceptibility to bipolar disorder by influ- encing the balance of certain neurotransmitters in the brain (Hashimoto et al., 2005; Kuratomi et al., 2008).
A new and particularly intriguing line of research aimed at understanding the cause of mood disorders stems from the diathesis–stress model. Recent research shows that a diathesis (biological predisposition) leaves some people particularly vulnerable to certain stress hormones. Adverse or traumatic experiences early in life can result in high levels of those stress hormones, which in turn increases the likelihood of a mood disorder later in life (Bradley et al., 2008; Gillespie & Nemeroff, 2007).
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mania A mood disorder characterized by euphoric states, extreme physical activity, excessive talkativeness, distractedness, and sometimes grandiosity.
bipolar disorder A mood disorder in which periods of mania and depression alternate, sometimes with periods of normal mood intervening.
Psychological Factors Although a number of psychological factors are thought to play a role in causing severe depression, in recent years, researchers have focused on the contribution of maladaptive cognitive distortions. According to Aaron Beck (1967, 1976, 1984), during childhood and adolescence, some people undergo wrenching experiences such as the loss of a parent, severe difficulties in gaining parental or social approval, or humiliating criticism from teachers and other adults. One response to such experience is to develop a negative self-concept—a feeling of incompetence or unworthiness that has little to do with reality, but that is maintained by a distorted and illogical interpretation of real events. When a new situation arises that resembles the situation under which the self- concept was learned, these same feelings of worthlessness and incompetence may be acti- vated, resulting in depression. Considerable research supports Beck’s view of depression (Alloy, Abramson, & Francis, 1999; Alloy, Abramson, Whitehouse, et al., 1999; Kwon & Oei, 2003). Therapy based on Beck’s theories has proven quite successful in treating depression. (See Chapter 13, “Therapies.”)
Social Factors Many social factors have been linked with mood disorders, particularly difficulties in interpersonal relationships. In fact, some theorists have suggested that the link between depression and troubled relationships explains the fact that depression is two to three times more prevalent in women than in men (National Alliance on Mental Illness, 2003), because women tend to be more relationship oriented than men are in our society (Ali, 2008; Pinhas, Weaver, Bryden, Ghabbour, & Toner, 2002). Yet, not every person who experiences a troubled relationship becomes depressed. As the systems approach would predict, it appears that a genetic predisposition or cognitive distortion is necessary before a distressing close relationship or other significant life stressor will result in a mood disorder (Wichers et al., 2007).
Person–Situation The Chicken or the Egg? It is sometimes difficult to tease apart the relative contribution of the person’s biological or cognitive tendencies and the social situation. People with certain depression-prone genetic or cognitive tendencies may be more likely than others to encounter stressful life events by virtue of their personality and behavior. For example, studies show that depressed people tend to evoke anxiety and even hostility in others, partly because they require more emo- tional support than people feel comfortable giving. As a result, people tend to avoid those who are depressed, and this shunning can intensify the depression. In short, depression- prone and depressed people may become trapped in a vicious circle that is at least partly of their own creation (Coyne & Whiffen, 1995; Pettit & Joiner, 2006). ■
Cognitive distortions An illogical and maladaptive response to early negative life events that leads to feelings of incompetence and unworthiness that are reactivated whenever a new situation arises that resembles the original events