How Trauma Impacts the Nervous System

Why is understanding the nervous system important? Understanding how our nervous system operates has been incredibly useful to me personally and as a clinician in better understanding what happens in my own body as well as what is happening for my clients. Understanding our nervous system can help us meet ourselves with more kindness, compassion, and understanding, as well as meet our own needs. In this blog post, Edmonton-based therapist, Danielle Lall, explains what the nervous system is, how trauma can affect it, and ways to regulate yourself.

What is the Nervous System

Our autonomic nervous system is like our body's command center, it regulates and directs all movement, thought, and autonomic functions. There are two branches of the nervous system, the sympathetic nervous system, and the parasympathetic nervous system. The sympathetic nervous system works like a car's gas pedal. It triggers the fight-or-flight reaction, which gives the body a rush of energy so it can react to what it thinks are threats. The parasympathetic nervous system slows down the body's movements. It activates the "rest and digest" response, which calms the body down when the danger has passed. The sympathetic nervous system and the parasympathetic nervous system function together in a hierarchy with three systems: hyperarousal (fight or flight), the window of tolerance (connection and safety), and hypoarousal (shutdown and collapse).

The Window of Tolerance. Concept developed by Dan Siegel. Image by Kiara Mucci.


The hyperarousal zone is controlled by the sympathetic nervous system, which turns on our survival defenses (fight or flight). When we detect danger, our sympathetic nervous system kicks in, preparing our bodies to move so we can either fight the threat or run away from it. As a result, we experience increased sensations, anxiety or panic, hypervigilance, and racing thoughts.

Window of Tolerance

Our window of tolerance is a way to think about how much we can take or how much we can handle. Specifically, it refers to how much we can tolerate strong emotions on the sympathetic end and being bored, numb, or sad on the parasympathetic end. We are in our window of tolerance when we are present, calm, grounded, and engaged. The window of tolerance is a state in which both our sympathetic nervous system (fight or flight) and our parasympathetic nervous system (rest and digest response) work in harmony. This lets us function at our best, and deal with daily demands because we have access to our full capabilities. Being in this zone also allows us to experience a sense of safety and connection to others and ourselves.


Our bodies can also become hypoaroused in response to stress. When we are in the hypoarousal zone, our parasympathetic nervous system starts to work to slow us down. This happens when the body is under too much stress and our nervous system shuts us down to keep us from being overloaded. When we are in this hypoarousal zone, we can feel exhausted, unable to move much, numb to our feelings, and disconnected to ourselves. This is our bodies' way of protecting us from suffering more pain than we can handle.

These defensive states have evolved for survival to keep us safe, when we need protection. When our nervous system detects features of danger, our automatic structures become activated. We do not consciously consider entering these defensive states because this is an automatic and unconscious process that occurs. For example, if we run into a bear, we detect this as a threat, and our nervous system will decide what the best option is for survival. This triggers the defensive response in the body necessary to survive - fight, flee, or freeze. Today, our threats appear to be less urgent and more long-term. While we are not concerned with encountering bears, we do worry about having enough money to pay the bills and ensuring that they are paid on time, as well as performing well at work to ensure job security, and many more. Even though the stressors are different our bodies respond in the same ways.

How Trauma Affects the Nervous System

Trauma is when an event, a series of events, or a set of enduring conditions that overwhelms a person's ability to cope and/or is seen as a threat to safety or survival, causing automatic defense reactions. The definition of trauma is evolving as we come to realize that it is not the actual events that characterize trauma, but rather how a person is affected by it. 

Everyone's nervous system moves between all three arousal zones discussed above. The difference is that people with well-balanced nervous systems can return to their "window of tolerance" and be able to calm themselves after a stressor. Those that have experienced trauma tend to have a dysregulated nervous system, meaning they can get stuck in these zones of hyperarousal or hypoarousal for an extended period of time. When the nervous system gets stuck in either one of these defensive states, it’s no longer in the window of tolerance and therefore outside the window of optimal functioning. Our brain's prefrontal cortex, which is involved in impulse control, decision-making, and emotion regulation, shuts down when we are outside of the window of tolerance. When our nervous system gets stuck in the hyperarousal zone, it leaves us in a heightened state of fear and protection. Being stuck in this zone for extended periods of time can lead to anxiety, restlessness, hyperactivity, panic, and anger. The body finds it extremely taxing to remain in this defensive state since it requires a great deal of energy. Our bodies are not intended to stay in state for a long time. Our nervous system can also get stuck in the hypoarousal zone, which can cause fatigue, depression, and an overall feeling of being disconnected with ourselves and the others.

This does not mean that those who have experienced trauma are permanently stuck in one of these zones; rather, trauma shrinks their window of tolerance, making it harder to maintain a regulated and calm state. This is because after experiencing trauma, we are more vigilant to possible threats and therefore fluctuating more often through hyperarousal and hypoarousal zones.

Ways to Regulate the Nervous System

Working on regulating the nervous system can help regain a sense of calm and safety after trauma. There are many ways to help regulate the nervous system and get us back into our window of tolerance. Understanding what works and when we need it is the tricky part. Sometimes certain activities can be grounding or down-regulating, and other times they can be stimulating. Find what works best for you by experimenting with different options. Working with a counsellor or therapist can help you identify which of the activities work for your nervous system. By practicing grounding activities regularly when we are calm, we can increase our ability to do so when we start to feel overwhelmed. Here are some of the things that have helped me and my clients in the past and that you might find useful as well.

  1. Deep breathing. Breathing is an excellent way to reconnect with your body and begin to move out of this defensive state. When we extend our exhale longer than we inhale, our parasympathetic nervous system (rest and digest) is stimulated. This is an excellent way to move from hyperarousal back into a more regulated state.
  2. Movement. Physical movement and exercise can be so effective for bringing us back into our window of tolerance. Intense physical activity can help release pent-up frustration or anxiety if we are in the hyperarousal zone; however, others find lower-intensity movement can be helpful in bringing their system back into a more regulated state. Mildly stimulating exercises, such as swaying or rocking oneself, can help us get out of a hypo-aroused state and return to our body.
  3. Engaging with our senses. Paying attention to the sounds, smells, and tastes around us, as well as the things we can physically feel and see, brings us into the here and now. Using our senses to connect with the here and now is an excellent way to regulate ourselves.
    • Listening to upbeat, stimulating music can increase arousal.
    • Listening to calming music can decrease arousal.
  4. Find safe connections. When we are in a safe environment with a safe and calming person, our nervous system can regulate and come back into its window of tolerance. When our nervous system is in close proximity to someone who is within their tolerance window, we can co-regulate, which helps to regulate each other's nervous systems. If you notice yourself withdrawing from social connection or isolating yourself because you are a social being who heals in relationships, instead think about going to people who make you feel supported and safe.


There are many great ways we can learn to regulate our nervous system and bring it back into its window of tolerance when we find ourselves in a defensive state. The first step is to practice becoming aware of when we are in a dysregulated state and then begin practicing ways to bring our nervous system back into our window of tolerance that can help with nervous system regulation, allowing us to navigate through life feeling more grounded and connected to others. Developing a support network that includes a trained counsellor can help us heal and recover from trauma. If you are interested in working through trauma and learning more about how you can broaden your window of tolerance, I would be happy to work with you. Reach out to one of our Edmonton-based registered therapists today and start your healing journey.


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