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The Psychology and Physiology of Depression
Trauma and stressful events can disrupt the physiologic homeostasis of our bodies and brains. The physiologic stress response consists of neural and endocrine mechanisms whose function is to reestablish homeostasis. These mechanisms include the secretion of glucocorticoids (cortisol) and catecholemines (epinephrine and norepinephrine). Once an external event has ceased to be a stressor or threat to a human organism, an integrated system of negative feedback loops inhibits the continued production of these hormones and effectively shuts down the stress response. These mechanisms are adaptive in the sense that they ensure the survival of the organism by reestablishing homeostasis. But prolonged exposure to real or perceived stressors can trigger prolonged secretion of stress hormones, thereby disrupting the feedback systems and causing a cascade of pathogenic events. The stress response is a double-edged sword. An acute stress response can protect an organism from external threats and reestablish homeostasis. But a chronic stress response can cause the body's defenses to become damaging rather than protective and to result in various disorders. Acute stress responses are adaptive. Chronic stress responses are often maladaptive and pathogenic.
In "Depression as a Mind-Body Problem," I characterized major clinical depression as a disorder resulting from a maladaptive chronic stress response (Glannon 2003). Specifically, I argued that depression often results when our beliefs and emotions are out of proportion to the true nature of external events. The mind prolongs rather than constrains the physiologic stress response. Depression is not a disorder of the brain alone or the mind alone, however. Endocrine and immune dysfunction can contribute to the dysfunction in the brain and central nervous system that are involved in depression. Moreover, the contents of the mental states that initiate the sequence of events leading to depression are reflections of the person's natural and social environment. Thus, a satisfactory account of depression requires an analysis of the interconnections among the central nervous, endocrine, and immune systems, as well as the mind and the environment. All of these factors support the description of depression as a psychoneuroimmunologic disorder.
Mike Martin (Martin 2003) and Thomas Fuchs (Fuchs 2003) discuss important aspects of depression that I did not elaborate in my paper. Martin argues that I fail to distinguish between depression as a mood and depression as a disorder. This is pertinent to the distinction evolutionary psychiatrists draw between moods that are adaptive and moods that are maladaptive. In contrast to my negative characterization of depression, Martin also makes a case for the positive [End Page 265] contributions of depression to meaningful life. Fuchs explores the notion of the brain as an organ of translation enabling patients to have meaningful subjective experience. The emphasis on subjectivity has important implications for potential preventive and therapeutic interventions for depression. For whether a person perceives an external event as a stressor may play a crucial role in the physiologic stress response. I will address the main points of these two authors in turn.
Contrary to what Martin claims, I explicitly defined chronic depression as an affective (mood) disorder. My focus was on the clinical definition of major depression as a moderately severe to severe chronic disorder. It consists of affective, cognitive, and even physical dysfunction that interferes with a person's ability to carry out the normal tasks of daily life. This characterization of major chronic depression distinguishes it from milder forms of depression, such as dysthymia. Because these milder forms do not involve the same type or degree of dysfunction as more severe forms, they are not appropriately characterized as pathologies. For this reason, I focused on Nesse's (2000) discussion of depression rather than on his discussion of low mood. In fairness to Nesse and Stevens and Price (2000), not all forms of depression are pathologic according to the evolutionary view they defend. Some passive aspects of mild depression may be useful in alerting us to dangerous or wasteful behavior. It does seem plausible to describe depressed moods as falling along a continuum from those that...