The Effect of Trauma on the Nervous System

body-based therapies healing from trauma the window of tolerance trauma and the nervous system

Trauma dysregulates our nervous system to the point where we can no longer regulate our experiences and emotions.


Trauma can be incredibly debilitating and significantly impacts the quality of life of trauma survivors. Here at Rewire Therapy, we are passionate about providing practical tools and techniques on how to heal trauma. Learn more


 Welcome reader,


This article aims to offer insights into some of the factors at play in our bodies, particularly our nervous systems, following trauma. We’ll begin by discussing the nervous system to clarify terms, then dive into the Window of Tolerance, which refers to the window within which optimal states of arousal occur where emotions and experiences feel tolerable; here we will address how it helps us understand why we feel so overwhelmed following trauma and how this leads to nervous system dysregulation.


What is the Nervous System?


The nervous system is the body’s command center and it regulates and directs all movement, thinking, and autonomic functioning. The autonomic nervous system is split into two divisions, the sympathetic nervous system and the parasympathetic nervous system.


The sympathetic nervous system is responsible for regulating the bodily response associated with the ‘fight or flight’ stress response (McCorry, 2007). The sympathetic nervous system is triggered in situations your brain deems dangerous and its job is to prepare your body for physical activity to allow you to either fight the danger or flee from it.


The activation of the sympathetic nervous system initiates an increase in the flow of oxygenated and nutrient-rich blood to your skeletal muscles and an increase in hormones, specifically adrenaline (epinephrine) and noradrenaline (norepinephrine), which act on the brain- increasing arousal and selective attention, as well as hypervigilance (McCorry, 2007; Lipov, 2013).


On the other hand, the parasympathetic nervous system is responsible for regulating the ‘rest and digest’ bodily response. The parasympathetic nervous system responds in situations of safety to conserve and store the energy needed for basic bodily functions including digesting, urinating and reproduction (McCorry, 2007). Under normal circumstances, these two systems function in harmony with a continual and healthy fluctuation between the two responses in order for our bodies to achieve a state of homeostasis throughout our daily lives.


The Window of Tolerance


On a day-to-day basis, we experience fluctuations between the activation of our sympathetic nervous system and the parasympathetic nervous system. When we experience the stress of sitting in traffic on the way to work, our SNS is activated, followed by a sense of relaxation when we arrive on time. When we are enjoying a relaxed lunch break or watching a movie on the couch after work, our PNS is activated.


While we may think that our sympathetic nervous system is only activated during periods of intense danger, we in fact experience it on a daily basis. These experiences are not perceived as traumatic or fundamentally dangerous because they fall within the Window of Tolerance (Siegel, 1999).


The Window of Tolerance model proposes that between the extremes of sympathetic activity and parasympathetic activity, there is a window within which optimal states of arousal occur where emotions and experiences are experienced as tolerable (Corrigan et al., 2010). Within the Window of Tolerance, we are able to regulate our emotions and in turn regulate our nervous system to a place of homeostasis.



Trauma and the Nervous System


Trauma is defined as a significant stressor where actual or threatened death, serious injury, or sexual violence has occurred (American Psychiatric Association, 2013). By definition, traumatic experiences fall outside of the normal range of daily human experience, and thus these experiences fall outside of the Window of Tolerance (Lipov, 2013). Trauma pushes us to the point where it is very challenging to regulate our experiences and emotions, and our nervous system becomes dysregulated (Corrigan et al., 2020).


Sympathetic nervous system activity is pushed to a point of hyperarousal where individuals are in a permanent ‘fight or flight’ state and cannot experience heightened emotions or physiological arousal without becoming overwhelmed (Corrigan et al., 2010).


Other survivors of trauma may fall on the alternate side of the Window of Tolerance to parasympathetic hypo-arousal where individuals are in a permanent state of submission or ‘freeze’ response characterized by nonreactive, disconnected, and depressed affect (Corrigan et al., 2010).


There are many filtering systems within the nervous system that help your brain to autonomically decide whether a situation is safe or not, and tell your body how to respond accordingly. Trauma expert, van der Kolk (2004), states that it is damage to a trauma survivor’s filtering systems in the nervous system that results in difficulties distinguishing between relevant and irrelevant stimuli that overwhelm a survivor’s coping mechanisms. This causes a breakdown in the normal homeostatic self-regulating systems and results in nervous system dysregulation (van der Kolk, 2004)).


The nervous system dysregulation results in a neuronal change, changes to the HPA axis and hormonal level alterations which all contribute to stress response, arousal regulation and even immune system functioning (van der Kolk, 2004). When the behaviors following this dysregulation of the nervous system become chronic, we see cases of PTSD (Sherin & Nemeroff, 2011).


There are many small and easy interventions available to help fix the nervous system dysregulation following trauma. Want to learn how to fix nervous system dysregulation? Read our guide here: Nervous System Dysregulation and How to fix it


  1. American Psychiatric Association. (2013). Diagnostic and statistical manual of mental disorders (5th ed.). 
  2. Corrigan, F., Fisher, J. and Nutt, D., (2010). Autonomic dysregulation and the Window of Tolerance model of the effects of complex emotional trauma. Journal of Psychopharmacology, 25(1), 17-25.  
  3. Lipov, E., (2013). Post Traumatic Stress Disorder (PTSD) as an Over Activation of Sympathetic Nervous System: An Alternative View. Trauma & Treatment, 03(01).  
  4. McCorry, L. (2007). Physiology of the Autonomic Nervous System. American Journal Of Pharmaceutical Education, 71(4), 78.  
  5. Sherin, J., & Nemeroff, C. (2011). Post-traumatic stress disorder: the neurobiological impact of psychological trauma. Dialogues In Clinical Neuroscience, 13(3), 263-278. 
  6. Siegel, D. (1999). The Developing Mind: Toward a Neurobiology of Interpersonal Experience. Guilford Publications, Inc.
  7. van der Kolk, B. A. (2004). Psychobiology of posttraumatic stress disorder. In J. Panksepp (Ed.), Textbook of biological psychiatry (pp. 319–344). Wiley-Liss.

Want Practical Strategies For Healing The Trauma-affected Nervous System?

If you find these articles helpful and want practical therapies you can use to begin fixing nervous dysregulation today you may be interested in exploring our top-rated guided programs:

Vagal Toning Program

Integrating Polyvagal Theory into 10-minute therapies that gently tone the vagus nerve after trauma

Learn More

Trauma-Informed Yoga Program

Safely integrate reparative trauma-informed yoga postures to facilitate 'tissue memory' release

Learn More

Somatic Therapies For Trauma Program

Tune into your body, develop your somatic awareness, and find a sense of groundedness.

Learn More