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Defensive Response to Remembered Threat

When the limbic system activates the ANS to meet the threat of traumatic event, it is normal, healthy, adaptive survival response. When the ANS continues to be chronically aroused even thought the threat has passed and has been survived, that is PTS.  The traumatic event seems to continue to float free in time, rather than occupying its locus in one’s past, often coming unsought and intrusively into the present perception as if it were actually occurring now.  However, each time he encountered one he continued to respond in his mind and body as if he were being, or about to be, attacked again).

Within the limbic system are two related areas that are central to memory storage:  the hippocampus and the amygdala.  The last few years have produced a growing body of research that indicates these two parts of the brain are centrally involved in recording, filing, and remember traumatic events (Nadel & Jacobs, 1996; van der Kolk, 1994, among others).  The amygdala is known to aid in the processing of highly charged emotional memories, such as terror and horror, becoming highly active both during and while remembering a traumatic incident.  The hippocampus, on the other hand, gives time and space context to an event, putting our memories into their proper perspective and place in our life’s time line.  Hippocampal processing gives events a beginning, middle and, an end.     This is very important with regard to PTSD, as one of its features is a sense that the trauma has not yet ended.  It has been shown that the activity of the hippocampus often becomes suppressed during traumatic threat; its usual assistance in processing and storing an event is not available (Nadel & Jacobs, 1996; van der Kolk, 1994 among others).  When this occurs, the traumatic event is prevented from occupying its proper position in the individual’s history and continues to invade the present.  The perception of the event as being over and the victim as having survived is missing.  This is the likely mechanism at the core of the quintessential PTSD symptom of “flashback” – episodes of reliving the trauma in mind and or body.”  (Adapted from Rothschild, B. 2000) 

 

 

Survival and the Nervous System 

"Arousal, and therefore traumatic hyperarousal, is mediated by the limbic system, which is located in the centre of the brain between the brain stem and the cerebral cortex.  This part of the brain regulates survival behaviours and emotional expression.  It is primarily concerned with tasks of survival, such as eating, sexual reproduction, and the instinctive defenses of fight and flight.  It also influences memory processing:

      The limbic system has an intimate relationship with the autonomic nervous system (ANS).  It evaluates a situation, signaling the ANS either to have the body rest or to prepare it for effort.

      The ANS plays a role in regulating smooth muscles and other viscera: heart and circulatory system, kidneys, lungs, intestines, bladder, bowel, pupils.  It’s two branches the sympathetic branch (SNS) and the parasympathetic branch (PNS)usually function in balance with each other.  When one is activated, the other is suppressed.

      The SNS is primarily aroused in states of effort and stress, both positive and negative.  The PNS is primarily aroused in states of rest and relaxation.

      The limbic system responds to the extreme of traumatic threat, by releasing hormones that tell the body to prepare for defensive action:

      Following the perception of threat, the amygdala signals an alarm to the hypothalamus (both structures in the limbic system) that turn on two systems: (1) activation of the SNS, and (2) the release of corticotropin-releasing hormone (CRH). Those actions continue, each with a separate, but related, task.  First the activation of the SNS will, in turn, activate the adrenal glands to release epinephrine and norepinephrine to mobilize the body for fight or flight.  This is accomplished by increasing respiration and heart rate to provide more oxygen, sending blood away form the skin and into the muscles for quick movement." 

"At the same time in the other system, the CRH, is activating the pituitary gland to release adreno-cortico-tropic hormone (ACTH), which will also activate the adrenal glands, this time to release a hydro-cortisone, cortisol." 

"Once the traumatic incident is over and/or the fight or flight has been successful, the cortisol will halt the alarm reaction and the production of epinephrine/norepinephrine, helping to restore the body to homeostasis." 

"This system is called the HPA axis.  The reason it is important to trauma work is that in PTSD something goes wrong with it.  Rachel Yehuda (Yehuda et al. 1990) pioneered the discovery that in those with PTSD the adrenal glands do not release enough cortisol to halt the alarm reaction (see Figure 1.2).  Several studies have shown that individuals with PTSD have lower cortisol levels than controls, even those with other psychological problems like depression.  One conclusion that can be drawn from this evidence is that on a chemical level the continued alarm reaction typical of PTSD is due to a deficiency of cortisol production.  However, whether it is a purely biological process or is influenced by perception in the limbic system is not known.  While the low cortisol levels are documented in PTSD, their cause is still a question." 

"One area of interest with regard to the HPA axis and cortisol is the freezing response to traumatic threat.  When death may be imminent, escape is impossible, or the traumatic threat is prolonged, the limbic system can simultaneously activate the PNS, causing a state of freezing called tonic immobility like a mouse going dead when caught by a cat, or stiff, like a deer caught in headlights (Gallup & Maser, 1977).  The chemical picture that causes the freeze must be linked to the HPA.......'"

Porges work has demonstrated that the 'fight & flight' dynamic is a cascading reciprocal dynamic starting with Fight and moving through to Faint as each successive defensive dynamic is deemed at a neuroceptive' to be inadequate to protect.

These nervous system responses fight, flight, freeze, fear (tonic immobility,and faint are much more complex than simple reflexes.  As the dynamic moves from high arousal, high blood pressure 'Freeze' to low arousal, low blood pressure tonic immobility  the victim of trauma concurrently enters an altered reality (dissociates) 

"Time slows down and there is no fear or pain.  In this state, if harm or death do occur, the pain is not felt as intensely.  People who have fallen from great heights, or been mauled by animals and survived report just such a reaction.  The freeze response might also increase chances of survival.  If the cause is an attack by man or beast, the attacker may lose interest once the prey has gone dead, as a cat will lose interest in a lifeless mouse." 

"Limbic stem/ANS responses are instantaneous, instinctive responses to perceived threat.  They are not chosen by thoughtful consideration.  Many who have suffered trauma feel much guilt and shame for freezing or going dead and not doing more to protect themselves or others by fighting back or running away.  In those instances , understanding that freezing is automatic often facilitates the difficult process of self-forgiveness.  (Adapted from Rothschild, B. 2000)

Divisions of the Brain

It is easy to conceptualize what the brain looks like (see Figure 2.2).  Make your right hand into a fist, holding it upright.  Your right wrist represents the brain stem, your fist the midbrain and limbic system.  Now take your left and cover your right fist.  That is the cerebral cortex, the outer layer of the brain.   

    The brain stem, sometimes referred to as the reptilian brain, regulates basic bodily functions such as heart rate and respiration.  This region of the brain must be mature at birth for an infant to survive.

    The limbic system is the seat of survival instincts and reflexes.  It includes the hypothalamus, which is responsible for maintaining body temperature, essential nutrition and hydration, rest and balance.  The limbic system also regulates the: autonomic nervous system, mediating smooth muscle and visceral responses to stress reactions of fight, flight and freeze

    Two other limbic system regions, the hippocampus and the amygdala are especially pertinent to understanding traumatic memory.  Both the hippocampus and the amygdala consist of two lobes, one on each side of the brain.  Both the structures are integral to processing information transmitted from the body on the way to the cerebral cortex.

    The amygdala processes and then facilitates the storage of emotions and reactions to emotionally charged information. (Rothschild, 2000)

 

 

 

Lindy Bearup lindybearup@gmail.com
 

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but today well lived - makes every yesterday a dream of happiness and every tomorrow a vision of hope"
old Sanskrit proverb.