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How individuals respond to traumatic events may partially come down to the differences between how they process information and feeling. Those individuals who are able to keep talking to themselves while a traumatic event is occurring, and who keep planning for a possible future, are engaging the left side of their brain. These persons process sequentially and logically. They still feel intense fear, but their left-brain approach to understanding prevents them from being overridden with terror. Those individuals who process from the right side of their brain experience the world from a more sensory, emotion-laden place. They receive the whole image of the event all at once, with emotion, sensation, and perception heightened. They cannot, in the instant of terror, manage a sequential understanding of the event, nor can they decide in a rational or logical manner what to do next in order to protect themselves. They no longer experience the world through the filters of their cerebral cortex and are entirely, at the moment of trauma, in the right side of the brain. They are, in other words, in a place of "speechless terror." Individuals who experience this are far more likely to develop PTSD.9 The brain is exquisitely organized into three basic and highly interrelated parts and functions. The brain stem and hypothalamus monitor regulation of one's internal environment and the fight or flight mechanisms. The limbic system balances the internal and external worlds and processes raw emotion. The neocortex analyzes and solves problems and is the part of the brain through which we largely interact with the external world. Together these parts of the brain coordinate the unconscious and conscious functions of feelings, thoughts, memories, communication, and actions.
One of the functions of the limbic system, the center of emotions, is to store fear-based experiences. Rapid and accurate access to experiences of fear and its associations is highly necessary for survival. For example, if a person walks down a forest path and sees a long cylindrical object lying across the path, he may gasp, stop quickly, or run away. The reaction to the object happens before the neocortex gives any information about what that object might be. Part of the limbic system, the amygdala, records fearful experiences and feelings in intense sensory detail, and alerts the person to the possibility that the object is a snake, long before the word "snake" occurs in the person's left-sided cortex. The amygdala also sends messages to the hypothalamus to activate the hypothalamus-pituatary-adrenal (HPA) axis, the fight or flight mechanisms, so that the person will stop, look, and get ready to run, if necessary, before even knowing what the object is.
Under ordinary circumstances, high levels of cortisol in the bloodstream, an indicator of stress, will activate the process of homeostasis in the body. From the Greek meaning "to keep things the same," homeostasis is a complex process wherein the body maintains a finely tuned balance between all the systems that it needs to survive. After the danger (real or perceived, external or internal) has passed, the neurohormonal system will usually right itself. However, the neurohormonal systems of persons who experience PTSD are often stuck in the fight or flight mode, remaining hypervigilant or hyperalert. Clinically high levels of the hormones cortisol and norepinephrine result in hypervigilance and its related wariness and neural hyperreactivity. Another way that this break in the neurohormonal cycle manifests is as a cortisol and norepinephrine burnout. In this type of stress hormone burnout, clients may experience numbness in parts of their bodies, lethargy, and depression. PTSD clients may present with one or both of these conditions.
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