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Overview
The neurobiology of encoding trauma is discussed in terms of changes to the structures and functions of neurobiology. This article focuses on Psychological trauma, as opposed to physical trauma, traumatic brain injury, or intracranial trauma.

Neurobiological correlates of encoding psychological trauma include patterns of changes in the activity of neurological networks, alterations in specific aspects of neurobiological processes, and neurobiological structural changes that occur in response to psychological trauma.

Psychological trauma refers to the outcome of one or more psychological stressors that exceed the psyche’s available resources to cope with the stressor or stressors. Psychological stressors can be imagined, learned about, witnessed, or directly experienced. Not all psychological stressors lead to psychological trauma. There are biological, psychological, and socio-cultural factors that mediate and moderate the effect of psychological stress and its contribution to, or etiology of, psychological trauma.

Psychological trauma can often be observed as patterned changes in neural activity by way of fMRI and other direct and indirect neuroimaging techniques, due to the neurobiological changes from a traumatic experience.

The Nervous System
The neurobiology of encoding trauma can be conceptualized in terms of the mind-body problem and the neural correlates of consciousness. Physiological responses in the nervous system that correlate with subjective experiences such as cognition, emotion, and sensation are central to the inquiry into the mind-body problem.

In addressing themes associated with the mind-body problem, Charles Darwin (1809-1882) tied emotions to biological responses, noting that the term Emotion predated its 1579 French use (émouvoir - "to stir up") and originates in the Latin emovere, meaning "to move out." Darwin wrote that the function of emotion was to initiate escape or avoidance behavior. Escape or avoidance behavior is now conceptualized in terms of the stress response, which includes the fight-or-flight response, the freeze response, and the tend and befriend response to psychological stress.

Fight-or-Flight Response
The Fight-or-flight response is a physiological response of increased Sympathetic nervous system functioning in which the body prepares to either fight or flee from a situation that is perceived as threatening. This response begins in the Amygdala when activated by fear. This then results in a cascading response to the Hypothalamus, then the Pituitary gland and Adrenal gland. The Adrenal medulla then produces hormones that lead to the release of Norepinephrine, increasing attention and anxiety, and Epinephrine, increasing blood flow, blood sugar and long-term memory ability.
 * Increased heart rate
 * Dilation of pupils
 * Slowing of digestion
 * Constriction of blood vessels
 * Shaking
 * Bladder relaxation

Freeze Response
The freeze response, or Freezing behavior, is a physiological immobilization reaction to a highly stressful event. The freezing reaction is commonly found in prey animals cornered by a predator. This reaction could prevent an attack through the prey animal feigning death. The physiological response involves increased heart rate deceleration and a lower sweat response to the stressful stimulus. The freeze response can happen before of after the Fight-or-flight response or alone. Early and multiple exposures to trauma is correlated with experiencing the freeze response.

Tend and Befriend Response
The Tend and befriend theoretical model describes evolutionary based stress response typically found in some female animals in which they tend to their offspring and befriend others for social support. The tend portion of the response is defined an evolutionary stress response in females to nurture and protect offspring. The physical contact between the offspring and mother after a threat increases oxytocin. This influx of oxytocin creates a calming effect in the offspring and mother. Safety behaviors towards offspring during threatening events may increase survival of the species. The befriend portion of the response is seeking the company of others in response to a threatening situation in order to get support, safety, and emotional comfort. During stressful situations women tend to rely on their social network in order to cope. Studies have shown that women are more likely than men to go to others to cope with stressors. Women are also more likely to seek out female social support and use these social networks to protect themselves from male aggression. Social groups can provide assistance with child care, the sharing of resources, and protection from threats.

Other Relevant Theories

 * Ivan Pavlov (1849-1936) developed the psychological "law" of the conditioned reflex, as well inquired into inescapable shock and "the reflex of purpose".
 * Stephen Porges (1945 - ) developed Polyvagal theory.

Neurological Correlates of Traumatic Stress
The human nervous system is crowned by the brain. The brain is conceptualized primarily in terms of its structure and function. Traumatic psychological stress can result in measurable changes to both the structure and the function of the human brain.

Structural Correlates of Psychological Trauma
Brain structures are primarily defined by hemispheres, lobes, and areas or regions, as well as by cell type (e.g. gray matter and white matter) and the structures of neurotransmission (e.g. by type of neurotransmitter and receptor). Structural correlates of psychological trauma may be observed at all structural levels from the hemispheric to the sub-cellular.

Functional Correlates of Psychological Trauma
Brain functions are primarily defined in terms of lateralization, lobes, cellular processes and biochemistry, as well as networks, and systems. Some networks become inhibited and some increase activity in response to psychological stress.