First, I’d explain that trauma is a disorder that develops from the dysregulation of the autonomic nervous system after experiencing an event that they felt impossible to scape or avoid suffering from. Because of that dysregulation, the two branches of the autonomic nervous system (ANS) —the one that acts automatically, without consent— will lose its balance. The 2 branches of the ANS —sympathetic and parasympathetic— have complementary functions and they normally work to compensate each other’s activation. The sympathetic is in charge of setting you in action while the parasympathetic is the one that calms you down, to keep you —and your organs— at rest.
The ANS is in charge of all the automatic functions of the body and of supplying energy to the internal organs including the blood vessels, stomach, intestine, liver, kidneys, bladder, genitals, lungs, pupils, heart, and sweat, salivary, and digestive glands.
The sympathetic nervous system (SNS) branch is constantly active at a basic level to maintain homeostasis by accelerating heart rate, widening bronchial passages, decreasing motility of the large intestine, constricting blood vessels, causing pupillary dilation, piloerection (goosebumps) and perspiration (sweating), and raising blood pressure, to name a few of its tasks. It is also responsible for the fight-flight (FF) response to prepare the system for protection and to keep us safe.
The parasympathetic nervous system (PNS) branch —sometimes called the rest and digest system— does its part in keeping homeostasis by conserving energy as it slows the heart rate, increases intestinal and gland activity, and relaxes sphincter muscles in the gastrointestinal tract. It’s also responsible for defensive actions sometimes called faint, immobilization, collapse, submit, and some other names. Some people think that it is responsible for “freeze” but that is inaccurate. Freeze is actually a defense that uses both branches at the same time.
Then, I’ll explain that in regular circumstances, we need a certain level of arousal —a state of increased physiological activity— to function in the world. The activation of the SNS & PSN goes up and down in a similar way that our heart rate oscillates. I’ll draw in a piece of paper how that looks for both branches. They look like:
After that, I’ll detail how the “window of tolerance” (WoT) is that range of activation where the ups and downs of our activation feel “normal.” We may feel stressed sometimes without having that stress impairing our productivity, while other times we could feel “down” but we’d still be able to do what we have to do in order to achieve our goals.
The way therapists use the WoT model is to help clients see graphically that sometimes the level of arousal or of hypoactivation goes beyond what is normally tolerable, and that’s when the emotional responses feel debilitating or impairing some of the functioning.
The following step is to explain that after the traumatization, the ANS will suffer from a series of alterations in its normal functioning keeping the person that suffers from trauma in a state of either:
heightened activity of the sympathetic (Hyper-arousal), or
a predominant activation of the parasympathetic (Hypo-arousal), or
a pervasive heightened activation of both (Rigid-Stuck or “Freeze”), or
a constant parasympathetic activity with the withdrawal of sympathetic activity (Tonic immobility), or
parasympathetic surge (Collapse immobility).
The WoT then will also get altered. It normally becomes narrower, and the levels of activation are higher (up or down) meaning that the picks of the oscillations will be bigger, and the tolerance for affect will get diminished too.
The most common use of the WoT model is for explaining hyper and hypo arousal.
HYPER-AROUSAL: if the stressors activate your sympathetic branch, you will experience emotions like anxiety, anger, fear, disorientation, etc., and your level of arousal will go up to levels that go beyond what you feel you can handle. Hyperarousal outside the WoT feels like overwhelm or helplessness and normally indicate the sequelae in your sympathetic from trauma.
HYPO-AROUSAL: when the stressors can’t be handled by the sympathetic, the parasympathetic will get activated in an extreme way to solve the sense of helplessness. Feelings of numbness, dissociation, confusion, low energy, disengagement, “depression,” to the point of hopelessness. This is a very dangerous state. It doesn’t seem like at first sight, but it has severe consequences to the rest of the body.
The typical model for the Window of Tolerance uses only one line to graph the ANS activation. It would be more clear to use one line for the sympathetic and another for the parasympathetic since there are people that suffer from both activations at the same time, and one of the most important characteristics of trauma is that it loses homeostasis because the sympathetic and parasympathetic stops balancing each other. Maybe in a future response. For now, I’ll end with a drawing of the well known WoT image.
The traditional WoT graph to describe how the person has become less tolerant to experience affect after trauma looks like this:
Responded originally at Quora How could you describe the “window of tolerance” to someone suffering from trauma?