The biology of routine stress responses and the biology of trauma are fundamentally different: Stress causes a cascade of biological and physiological changes that return to normal after the stress is gone or after the organism has established a new homeostasis. In contrast, in PTSD, the biological alterations persist well after the stressor itself has disappeared. The fundamental problem in PTSD is a "fixation of the trauma" (Janet, 1889; van der Kolk, 1985; Yehuda, 2002). Thus, the critical issue in understanding PTSD is: What keeps the organism from maintaining its homeostasis and returning to a nontraumatic state, and what causes these regulatory processes to break down?
Exposure to events that overwhelm the organism's coping mechanisms can damage the self-regulatory systems necessary to restore the organism to its previous state because of alterations in a variety of "filtering" systems in the central nervous system (CNS) that help distinguish relevant from irrelevant stimuli. As a result, traumatized individuals have difficulty engaging fully in current exigencies and distinguishing between what is threatening and what is safe. Traumatization produces the symptoms described in the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) definition of PTSD: intrusive reliving, numbing and hyperarousal, increased uncontrolled aggression against self and others, drug and alcohol abuse, depression, and chronic physical illnesses. Severe and prolonged childhood trauma has particularly dire consequences: Compared with normals, people with histories of severe child maltreatment showed a 4 to 12 times greater risk to develop alcoholism, depression, drug abuse, and suicide attempts, a 2 to 4 times greater risk for smoking, having had > 50 sex partners, leading to increased incidence of sexually transmitted disease; a 1.4 to 1.6 times greater risk for physical inactivity and obesity; and a 1.6 to 2.9 times greater risk for ischemic heart disease, cancer, chronic lung disease, skeletal fractures, hepatitis, stroke, diabetes, and liver disease (Felitti et al., 1998).
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