What are the physiological effects of terror? The word “stress” would come to mind to most people, that a strong emotion like terror comes from one of two things:
- a single, unpredictable, but extremely life-threatening event which triggers a fear of that event repeating whenever a person experiences a similar stimulus, or
- the chronic exposure to stress, causing a fear of the stressful events or even of stress itself.
What was an annoyance at first can escalate to anxiety under chronic exposure. Anxiety can then escalate to fear.
Updated: 12 Aug 2014
Hans Selye (1936) devoted his career to defining the physiological effects of stress. His accomplishment was probably greatest in providing researchers with good physiological models for studying stress. Since then a great deal of research has made the public aware of the deleterious effects of stress on the circulatory, nervous, endocrine, and immune systems. The physiology of terror is important to study because many of the symptoms of heart and endocrine disorders mimic responses to terror. For this reason, many people suffering from panic attack disorder and post-traumatic stress (disorder, PTSD) never get diagnosed and properly treated (van der Kolk 2005).
Perry et al. (1995) studied PTSD in infants, noting that the following traumatic experiences that can lead to PTSD in children: kidnapping, being abused, witnessing violent crime/abuse, or surviving other severe trauma.
Most people think that the “fight or flight” response (now modified by many to “fight, flight or freeze” response, Perry, 1997) is the only symptom of panic or PTSD, but in fact, the effects of terror on a person physiologically will differ depending upon who or what the situation is. Perry (1997) thought that females (“dissociation”) responded differently than males (“fight” or “flight”). This post will describe how people might respond in totally opposite ways to terror and discuss why this happens. Indeed, the “freeze” response was added because most children may show this behavior during a traumatic event or remembering one, but it also explains the adult response in certain circumstances (see “Fight, Flight, Freeze or Faint” (Striped Giraffe Press 2006). All physiological responses are probably tied to emotional responses, both conscious and unconscious. The mind and body are inextricably intertwined in Chinese medicine. Many symptoms may be relieved when this principle is applied by Western medical practitioners.
This post will discuss physiological aspects of the behaviors and emotions outlined in Types of PTSD. However, it will also describe PTSD in both children and adults to reflect the work done in “Special Case of Type I PTSD–Rejected Children.”
The behavioral/psychological symptoms are a way that the brain has for expressing the physiological symptoms, not just to the owner of those symptoms but also to all who may be watching the patient. The emotional state of the person may be a faster route for the person to detect that something is wrong, since most people are normally unconscious to many physiological symptoms. These emotional symptoms include the following:
- Helplessness, or :”freeze” response
- Fear or terror, leading to vigilance,
- Dissociation, sometimes leading to flight
- Panic, often leading to flight,
- Sudden, unexplained discomfort, leading to aggressive behavior
Each of these symptoms can be explained in terms of the physiological symptoms characterizing them. Some of these symptoms only become apparent to a person when they have practiced mindfulness.
The differences in expression of helplessness are due to different programs in the brain. I will refer to the types of PTSD as defined in Types of PTSD, which is different from how the DSM-V defines them. From my own observations, the Type I PTSD sufferer will display a parasympathetic response and the type II and type III sufferers, a sympathetic response. In other words, the latter two types will want to fight or flee, and the first one will freeze. The sympathetic response will cause an increase in heart rate, breathing rate, and blood pressure. The parasympathetic response will be exactly the opposite. However Type I PTSD is not completely opposite of Type II or III PTSD, when it comes to other symptoms.
The type I PTSD sufferer will often feel as if they cannot breathe (some complain of breathlessness), that something is suppressing their respiration. They have difficulty in moving their muscles of respiration. They will freeze because of several things happening. The brain’s motivation center (putamen) will block all activity of the red nucleus involved with motor output. This means that limb muscles cannot contract, but neither can gut muscles. Peristalsis comes to a halt. Metabolism is lowered. Critical nutrients do not make it to important tissues for action, like muscles, tendons, ligaments, and bones. We’re talking maintenance only. Furthermore, the motivation for running away disappears. The person may stand or sit still but will not feel as if they cannot move. They just lack the motivation, and almost feel as if something is keeping them, that they cannot move. With a superhuman effort, they could, but that drive to move is gone.
The type II and III sufferers will want to run unless greatly overpowered by their predator. Their motivation for running away is very high (putamen stimulates the red nucleus). Soldiers are taught to stand and fight and all of their energies will go into surviving, using the skills they were taught in these circumstances. In all cases, the sympathetic nervous system increases nutrient flow to critical tissues and shuts down activity in the gut. Metabolism is increased, but peristalsis also halts. There is increased flow of interstitial fluid as all basic ions and nutrients start to move throughout the body to supply as many tissues as are needed to be active.
Some soldiers complain that they do freeze and cannot move, even if it was too dangerous to stay. It is very likely that they are suffering from a combination of Type I and Type II or III and all types have to be treated in order to heal.
Why does the Type I PTSD sufferer freeze, whereas the types II and III sufferers run? I can answer that easily for the baby who is being terrorized by a mother who wants to kill it. The freeze response is typical of all baby mammals & birds (Gallup 1974). Schmidt et al. (2008) suggests that the freeze response is helpful when “additional attacks are provoked by movement.” Ethologists consider that the freeze response is quite common in animals when they fear they will be attacked (Roelofs et al. 2010). Young mammals and birds, who show the freeze response, are born either totally helpless or lack the skill/stamina to run away from a predator. Furthermore, many mammals are born with no scent so a predator cannot find them easily. If the baby moved when a predator was around, especially with the awkwardness typical of most young mammals, the predator would surely find it easily. Thus humans share with all baby mammals the tendency to freeze when afraid.
The freeze response will be expressed in all Type I PTSD sufferers who suffered early childhood trauma, especially if it was truly life-threatening. Van der Kolk (2005) mentions the freeze response as a characteristic of children suffering from maltreatment, as a result of what he proposes be called “developmental trauma disorder.” He suggested this name because not all children exposed to chronic, repeated trauma will show PTSD, as it was defined in the DSM-IV, but will show a complicated series of other characteristics, either as children or later, as adults (e.g. depression, suicide attempts, alcoholism, drug abuse, sexual promiscuity, domestic violence, cigarette smoking, obesity, physical inactivity, sexually transmitted diseases, heart disease, cancer, stroke, diabetes, skeletal fractures, liver disease).
Perry et al. (1995) and Perry (1997) caution that childhood trauma is much more potent than adult trauma because it happens when the brain is still developing. They cite evidence that the effects of early childhood trauma have far-reaching influence on the child throughout their entire lives. Indeed, this makes sense because the brain is laying down a lot of connections between neocortex and brainstem, linking conscious and unconscious parts of the brain. Since all this is happening at the earliest stages in post-natal life, one can suspect that these pathways are critical for creating “step one” in many behaviors, especially behaviors for which “step one” may be considered as “innate”, that they are inaccessible to the conscious mind. More importantly, one can also suspect that many pathways involved in creating us as social beings won’t be built until we can interact with other humans, which would by necessity be after birth.
Van der Kolk (2005) realized that a multitude of sensory triggers can occur in traumatized children, and when coupled with the fact that the trauma occurred during the period of rapid neurological development that characterizes the first three years of life, the group of characteristics that these children have will be much more complicated than what we normally see in people who suffer from PTSD as adults, e.g. the war veteran.
In this video, Dr. Robert Scaer speaks about the freeze response as having to be “discharged”, that wild animals and some tribesmen in the Amazon do this to get over the fear of the traumatic event. He says that we haven’t learned how to “discharge” this fear when we go into a freeze response. I dispute his conclusions, however, and think that the trigger of the freeze response is more important than the freeze response itself. The sufferer needs to figure out what the trigger is or will continue to have freeze responses.
Fear or Terror, Leading to Hypervigilance
A very prominent feature of PTSD in both adult and child is what is called the hyperarousal stage, where a person becomes hypervigilant. When they sense what was a trigger to their trauma in the past, they seem to over-react to it, often imagining the worst possible outcome when that expectation is unwarranted to the casual observer. Perry et al. (1995) suggest that hypervigilance, and its seemingly opposite response of dissociation (a feeling of disengagement with the reality of the situation–see below) result from a change in the brain. Hypervigilance or over-reaction may result from the brain using the same pathway again and again. These researchers also suggest that related to the “use-dependent” model is one where a neural pathway becomes sensitized to the point that less of a stimulus is needed over time to trigger a response. They seem to prefer the latter model to explain how hypervigilance and dissociation can be triggered over seemingly minor issues in traumatized children.
Sensitization of a neuron path may occur because when a traumatic experience activates a circuit, it can cause a change in the firing rate of a neuron and the quantity of neurotransmitter released.
Tom Cloyd (Healthy Place) implies that the freeze response is part of a feeling of dissociation associated with PTSD. Michele Rosenthal (Healthy Place) describes the feeling of dissociation often associated with PTSD.
There is another way to look at the role of the freeze response and dissociation. One might be able to generalize its appearance to anyone who is terrorized by someone they know. This may happen because a program based upon trusting someone gets built first in the brain. When a victim’s attacker betrays that trust, the brain has to develop new programs to handle that. When the betrayal is a sudden attack on a victim, the victim’s brain does not have time to develop a new program for this case and reverts to the program which assumes trust, i.e. blocks movement away from the “trusted” individual. This block might create a feeling of dissociation, since it blocks a lot of other senses whose input is critical for forming emotional responses.
All PTSD sufferers will display panic attacks. However the symptoms of a panic attack will be very different in different types of PTSD (ADAA). The physiological symptoms may include any of the following:
- increased/decreased heart rate (either Type I or Type II/III),
- breathing difficulties (e.g. shortness of breath, feelings of being smothered), sweating,
- trembling or shaking,
- nausea/distressed stomach,
- chills (sometimes shows up as teeth chattering)/hot flashes,
- numbness or tingling,
- feelings of unreality/detachment from oneself,
- losing control or going crazy, fear of dying
Other odd symptoms may include:
- pain in the gut, hands, feet, chest, head anywhere, including in tendons, ligaments, muscles, or bones anywhere, uterus, prostate, penis, groin, back
- inability to move rapidly, or at all, or with extreme difficulty
Children and adolescents may show slightly different symptoms from those shown in the adult (Massachusetts General Hospital, School Psychiatry Program & Madi Resource Center). Young children in particular, may not be able to describe their symptoms, but will display avoidance and other behaviors as symptoms, and only report physical symptoms and not psychological symptoms.
But some have noticed that there are more symptoms which may be an expression of panic. The Type I sufferer may display suppressed breathing, drop in heart rate. This person may also show more typical symptoms such as a sudden decrease in blood pressure that appears to feel like a hot flash. It is different from the typical post-menopausal hot flash, because it is always accompanied by the sudden difficulty in breathing. Doctors generally do not notice this difference nor the significance of the difference. Worse, the person increases breathing rate fairly quickly to make up for that sudden drop in breathing rate or sudden halt in breathing. Thus, this last behavior can be confused with a sympathetic response. Because the doctor ignores the fact that the person will also freeze, and have difficulty in moving for a brief time, no one recognizes how complex the problem is and the treatment will have less success. Van der Kolk (2005) raised the issue of the complexity of symptoms associated with early childhood trauma, as mentioned above.
These symptoms are not always cut and dried. The soldier who was imprisoned or tortured may show some of both sympathetic and parasympathetic responses in a panic attack. As time passes in a prison, the unknown person becomes more “known” and feelings of helplessness will take on the look of the type I PTSD sufferer. The same goes for the soldier hurt by friendly fire ( someone known to the soldier, or should be “known” to the soldier by rules of the band of brothers who are part of the armed forces, who should have been trustworthy).
The baby who has been repeatedly terrorized by a mother who did not want him/her will suffer panic attacks that almost defy the imagination. They will be closely related to the physiological responses that the baby had to each event. If exposed to toxins as one of the methods of attack, panic attacks will mirror much of the physiological responses that were happening at the time(e.g. itching in hands, feet, groin, back, or scalp, prickly skin, pain, itching or burning in the eyes, nose, throat, ears, inadequate muscle strength, low back pain). If a child was locked in a closet or shed, the panic attacks will mirror the physiological responses of that time (e.g. extreme sensitivity to certain smells, temperatures, humidity levels, the feel of a rope if tied up).
Sudden, Unexplained Discomfort
Typical of PTSD sufferers is the expression of strong emotions, often out of the blue. They may seem uncalled for in many cases, but they are triggered by unconscious memory of the terror attack. Because the memories are unconscious, the sufferer cannot attribute the emotions to any one thing or they attribute them to the wrong thing.
The cause of anger should be addressed as soon as it is displayed inappropriately, either in place or in strength, or it will progress to rage. Many people are described as having “anger issues” when in fact, that anger has already progressed to rage. Rage can be extremely difficult to detect, especially if it developed during babyhood, directed at a parent. Babies with rage, you ask? Yes, it is not expressed in the same way that adult rage is. Adult rage can develop during the teen and pre-teen years if the child is attacked sexually or physically at that time. However, if the child started life with terror attacks by a parent, then that child has had a lifetime of trying to hide rage because showing it would only call attention to them, and thus, more attacks.
Most psychiatrists prescribe drugs to patients with panic attacks and/or anger issues (see list at WebMD). In addition, some doctors found ketamine is helpful (see NPR Morning Edition for 25 Mar 2013, see discussion below). However, these drugs target the end points of a long chain of synapses and neural circuits involved in these problems, generally centers in the hypothalamus. Some panic attack drugs also seem to target some of the centers in the medulla as well, but no drug targets all the centers involved, simply because those centers may differ in all patients.
Rage may be an end point resulting from some centers not being able to turn off when their jobs are done because something else keeps stimulating them. Drugs for both panic attacks and anger control have enormous side effects as well, because they are not aimed at those other centers. The excess emotion is a lot like a very happily excited dog who wants to jump up on the person they are greeting. The drugs are similar to a person who tries to calm the dog down by grabbing its tail to stop its wagging. You have to embrace the whole circuitry to stop the attacks or deal with the anger issues. Often psychotherapeutic efforts do help because they at least attempt to work on parts of the entire circuitry. But sometimes you have to use other methods to find out where in the circuitry there is a problem.
I found that the best way to understand emotional or panic attacks as PTSD responses to terror is to use MRT (Muscle Reflex Testing, Applied Kinesiology, see MRT 1.0: Using MRT) to ask my brain what these emotional or physical events are associated with. It often takes time early in training to figure out what the cause is, but with time, the brain learns rapidly how to detect the cause. Once you figure out the cause, often the attack disappears, never to come back again, (when associated with that cause). But as cautioned elsewhere (MRT: Removing Toxins and Emotional Trauma), you will have to apply this same method to every memory, and every memory of a memory, and memory of a memory of a memory, making this very time-consuming for someone who suffered attacks as a baby.
Comment on ‘How An Unlikely Drug Helps Some Children Consumed By Fear’, reported on Morning Edition 25 Mar 2013, which tells us how ketamine has helped many children deal with abnormal fear.
NPR reporter Jon Hamilton describes a case of extreme fear in a child, now an adult. George McCann could remember always feeling enormous fear as a child. In fact, he seemed to have been born with it. He would have terrible nightmares when he slept, but would continue to feel threat by other people, even members of his family when awake. His response to this fear was aggression. He always felt so haunted by his fear that he also worried that something terrible was going to happen. Unfortunately it did happen when he was 12, and he had a violent enough outburst of rage that he was sent to a psychiatric hospital.
There, he was diagnosed with many disorders, from ADHD, obsessive compulsive disorder, to bipolar disorder. With each diagnosis came a different drug, none of which made him better. Some made him worse. When he reached his teens, a psychiatrist, Demitri Papolos, found out that George was part of a subset of children with bipolar disorder, called “fear of harm.” He describes how these children have particular characteristics: sleep disturbances with nightmares, feelings of pursuit or abandonment, extreme reactions when someone tries to control their behavior, including sudden, unpremeditated violence (“they’re not potential mass killers.”) They also cannot control thermoregulation, and overheat very easily. Papolos found that no antidepressants controlled fear and overheating, but ketamine did.
Past research showed that ketamine, used for anesthesia, could reduce severe depression extremely quickly, and prevent overheating at the same time. When George tried the drug, he felt a calm he had never felt before in his life.The drug does not seem to help everyone, but most of Papolos’ patients have felt dramatically better on the drug.
My Comments at NPR
Those who think ketamine is a solution are clearly not going after a cure. Yes, it is wonderful for stopping some symptoms. However, we have to remember that the conscious awareness of the symptoms does not mean that the entire neural circuitry is conscious. It inevitably depends upon unconscious circuits which cause an increase in heart rate, blood pressure and respiratory rate, sweating, and a general feeling of extreme discomfort, or any other aspect of fear (there are others, like teeth chattering, sudden feeling of being too cold, sudden feeling of being limp and not wanting to move, etc). All or fewer may be involved in other unconscious circuits associated with particular memories from the past. Worse for finding the cause, all memories are particulate (different senses involved, as well as who, what, when, where, are stored in different areas of the brain). When we become conscious of them, and even use them unconsciously, they have to be reconstructed to tell us what happened.
Because of the emphasis of doctors on the conscious aspects of fear, that child will be on ketamine for life. Everything that ever happens to you is saved in the brain. So even when you think that you have “grown out of” the condition, it is still there. Your brain has just discovered how to cover it up. Unfortunately, as we grow older, the cover-ups tend to fall apart, leading to breakdowns both physiologically and neurologically, creating all those symptoms that people think are caused by aging. Aging is not a cause of anything, it is only an effect of time.
The real cure comes from finding out why the child is so consumed by fear. That takes careful analysis and the recognition that unconscious brain processes may be at the root of the problem. Thus, talk therapy alone may not work very well, but careful monitoring of physiological responses using mindfulness, visualization (guided imagery), and muscle reflex testing (MRT or Applied Kinesiology) can help a child help himself. As the child grows up and is capable of learning more, as well as building a perspective, the child can ask more sophisticated questions of his own brain using MRT and learn how to disconnect the synapses which are being sent to very strong emotions in the amygdala of the brain when he has a conscious or unconscious memory triggering the symptoms.
Two interesting aspects of using these mind-body techniques are that
- the brain needs training to do it, and
- that the brain needs the simplest level of question to answer.
For the first point, training means practice, practice, practice using these techniques for asking permission to do everything. It becomes less necessary to ask first when mindfulness tells you when to wait and when to do what you want to do. Just as it takes a lot of practice to get a basketball into the hoop every time you shoot, from any angle, form any physiological state you have (e.g. coughing from a cold, too hot, too cold, emotional constraint, etc), it takes the same amount of practice and the same amount of learning by the brain to use mind-body techniques well. However, the rewards become obvious very early on in training, and more rapidly as training progresses.
For the second point, the technique helps you learn that there are levels or hierarchies in the brain for understanding most things. Mind-body techniques are accessing the lowest levels, deep in the brainstem where all such thought is unconscious. You learn that some of what you thought were simple questions are not that simple and have to be broken down even more.That is why training is necessary for that part of the brain to learn how to use the conscious levels to guide it to answers and vice versa. Very often children are much closer to the level of simplicity in thought used by the brainstem and can learn to use MRT effectively faster.
Hormones Do Not Explain Everything
Another commenter replied to my post that hormone imbalances could cause fear.
I replied with the following:
“Fear never comes from simply a hormone imbalance. Even when such an imbalance is found and treated with taking hormones, the conditions which led to the imbalance have not been addressed. Many people have to take the hormone for life for that reason. Sometimes the imbalance takes care of itself simply because the brain on its own, during normal repair cycles, finds the damage and fixes it. Sometimes, talking about another, supposedly unrelated event, suddenly gives the person insight which they never realize has something to do with the fear they have, but clears up the imbalance very quickly.”
“Most conditions leading to fear clearly come from the unconscious brain. They may be from inability to absorb certain essential nutrients, or even those which are classified as inessential simply because we need small amounts when compared with the “essential nutrients” (e.g. not enough iodine which affects the production of thyroid hormone). The hormone imbalance may come from toxins in the hypodermis which damage glands. It may also come from a block on full secretion by the brain because of damage elsewhere. Most damage in the brain is done either by toxins in the hypodermis which travel up into the brain with normal interstitial fluid flow, or by emotional trauma which affects every aspect of brain function.”
To which, she replied that “Media science, it is a wonderful thing to behold.” She said I was confusing two different emotions, fear and anxiety. She said that adrenal glands are located on the kidneys but not in the skin and not in the brain. She also said that “they secrete epinephrine, norepinephrine, dopamine, and cortisol.” She called aldosterone and epinephrine fight or flight hormones and that they were the hormones responsible for that “adrenaline” rush that comes when you feel afraid, making a point that the adrenal gland is controlled by the sympathetic nervous system, implying that sympathetic nerves did not supply the skin, nor were controlled by the brain.
If the comments had not been closed by the time I was notified of this last response, I would have posted the following:
The plastic toy, The Invisible Man (or Woman). It is a wonderful thing to behold.
However, if you learn anatomy from that toy and not in conjunction with physiology (or your physiology was taught by a physiologist who did not underscore the anatomy), and especially neuroscience, you will not understand how the activities within the adrenal gland are controlled by the central nervous system. The peripheral nervous system does not exist by itself. The CNS controls it.
No gland or other organ of the body can act without central nervous system input. Without the central nervous system, that adrenal gland cannot secrete anything. It gets innervated by both cranial and spinal nerves. Cranial nerve X will suppress its secretion. Spinal nerves coming from the T9 segment (of the group of T9-L2 segments) stimulate both secretion aldosterone (involved with the control of blood pressure), and epinephrine (involved with increasing the heart beat rate). Aldosterone is not considered a neurotransmitter of the sympathetic nervous system, although its activities are important for the control of blood pressure as part of the renin-angiotensin-aldosterone system. Thus the sympathetic nervous system can have an effect on the secretion of aldosterone.
Spinal nerves can act in local reflexes, but only when involved with motor neurons to skeletal muscle, or to all secretions and motility in the gut (the enteric nervous system). Thus, only the spinal column is necessary for these local reflexes to occur. However, spinal nerves do NOT act independently of the brain in secretion of epinephrine or aldosterone. They require brain input to do anything to the adrenal gland (Purves et. al. 2012). We learn about the sympathetic nervous system as a system separate from the brain and spinal cord, but it cannot function at all without input from both.
The roots of the sympathetic nervous system lie in the brain, in a very diffuse circuitry as part of the autonomic nervous system (a more inclusive system because it encompasses both the sympathetic and parasympathetic nervous systems). The autonomic control of glands and muscle, at its simplest level, one can argue, comes from the medulla, especially the reticular formation, but which gets signals from areas from all over the brain. The autonomic nervous system also includes areas higher up in the brain, with centers in the hypothalamus, pituitary, thalamus and amygdala.
Ketamine acts on these brain centers to suppress sympathetic output. However, it does not address all the sensory input which would cause the fight or flight response to begin with. Thus, it cannot be considered a cure for anything causing either fear or anxiety in a child, both emotions which trigger the sympathetic nervous response. Both emotions are signaled to the prefrontal cortex from the amygdala. The prefrontal cortex (the conscious part of the brain) is where those signals are interpreted either as fear or anxiety or both.
Purves et. al. (2012) also describes how emotions are intimately connected with all levels of visceral motor control (which includes the autonomic nervous system). Since emotions show up in typical reflexes such as blushing (involving sympathetic nervous innervation of the blood to the skin), sweating (also involving the sympathetic innervation of the skin and hypodermis), there is no doubt that the skin is also involved with the fight or flight response.
American Psychiatric Association. 1994. Diagnostic and statistical manual of mental disorders: DSM-IV. Washington, DC: American Psychiatric Association. ISBN 0890420610.
American Psychiatric Association. 2013. Diagnostic and Statistical Manual of Mental Disorders: DSM-V. Washington, DC: American Psychiatric Association. ISBN 978-0-89042-554-1
Gallup, G. G., Jr. (1974). Animal hypnosis: Factual status of a fictional concept. Psychological Bulletin, Vol 81(11), 836-853.
Perry, B. D., Pollard, R. A., Blakley, T. L., Baker, W. L., & Vigilante, D. (1995). Childhood trauma, the neurobiology of adaptation, and use-dependent development of the brain: How states become traits. Infant Mental Health Journal, 16(4), 271-291.
Perry, B. D. (1997). Incubated in terror: Neurodevelopmental factors in the “cycle of violence.” pp. 124-149 in Children in a violent society, Osofsky, J. D., Ed. New York, N. Y.: Guilford Press. [Freely available version is at The Child Trauma Academy].
Purves, D., Augustine, G. J., Fitzpatrick, D., Hall, W. C., LaMantia, A.-S., White, L. E. (2012) Chapter 21: The Visceral Motor System, Neuroscience, 5th Ed. Sunderland, MA: Sinauer Associates, Inc., Publishers.
Roelofs, K., Hagenaars, M. A., & Stins, J. (2010). Facing freeze: Social threat induces bodily freeze in humans. Psychological Science, 21(11), 1575-1581.
Schmidt, N. B., Richey, J. A., Zvolensky, M. J., & Maner, J. K. (2008). Exploring human freeze responses to a threat stressor. Journal of Behavior Therapy & Experimental Psychiatry, 39(3), 292–304.
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van der Kolk, B. A. (2005). Developmental trauma disorder: Toward a rational diagnosis for children with complex trauma histories. Psychiatric Annals, 35(5), 401-408.
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