Trauma and the Nervous System

nervous system

The nervous system is sometimes called the command system of the body. It controls reactions, thoughts, and movements and affects people’s digestion and senses. Trauma can greatly impact the nervous system, and Polyvagal Theory explains why this is.

Fight, Flight, and Freeze

When faced with something mentally or physically frightening, the acute stress response is triggered, which prepares the body to run or fight. The autonomic nervous system, which controls actions such as breathing and heart rate, comprises two separate systems: the sympathetic nervous system and the parasympathetic nervous system.

In dangerous situations, the sympathetic nervous system is activated by the release of stress hormones, which triggers the release of other hormones, including adrenaline and noradrenaline. This chain reaction increases heart rate, breathing, and blood pressure.[1]

After the danger has passed, the parasympathetic nervous system calms down the fight-or-flight response. This is also called the rest and digest system, which restores the body to equilibrium.

The Importance of the Vagus Nerve

Dr Stephen Porges, who developed the Polyvagal Theory, has proposed that there is one nerve that is of particular importance for the autonomic nervous system. The Vagus nerve is a long nerve that has two sides, the dorsal (front) and ventral (back), and is considered to have the widest distribution of nerves within the body.

The vagus nerve plays a key role in neuroception, the way the nervous system interprets cues of danger. The ventral side of the vagus nerve responds to feelings of physical safety and emotional connection, and the dorsal side responds to feelings of danger.

Responses to Danger

According to Polyvagal Theory, there is a hierarchy of responses built into the nervous system that the vagus nerve influences:

  • Immobilisation – also known as the freeze response, people respond to danger and fear by shutting down and becoming numb. Polyvagal Theory sees the immobilisation response as developing from the reptilian brain, the most primitive part of the human brain.
  • Mobilisation – the sympathetic nervous system takes over from immobilisation, helping people run or fight off the threat they face.
  • Social engagement – after facing a threat, people seek out social engagement and connection, which stimulates the ventral side of the vagus nerve and helps people rest and digest. This response is linked to the mammalian brain, as mammals rely on connection to thrive.

These responses can also be mixed, allowing for feelings of safety while engaging in social activities such as rough play and intimacy.[2] However, these responses do not always occur in order, and stressful events can affect how people react.

The Impact of Trauma

Trauma can have a huge impact on the body and the nervous system. When someone experiences a traumatic event, they may freeze and be unable to respond to the danger. After a traumatic event, the nervous system can pick up on more cues than ever in a person’s environment, and people can see danger in everything.

This is known as hypervigilance, in which people are more alert about their surroundings. It can cause many physical and mental symptoms, including:

  • Sweating
  • A rapid heart rate
  • Increased anxiety
  • Panic

For some people who have experienced trauma, triggers can cause them to move from social engagement to immobilisation. They may interpret small changes, such as facial expressions and tone of voice as dangerous and find themselves freezing up in an attempt to protect themselves. This is also known as dysregulation.

When the nervous system is regulated, people respond appropriately to external stimuli. For example, when a door slams, they may jump or flinch but quickly return to homeostasis once they realise there is no threat. Those with dysregulated nervous systems may hear a door slam and begin to panic as they think that danger is immediately present. On the other hand, they may also under-react and withdraw from the people around them.

Regulating the Nervous System

Working with the nervous system can help people to regain a sense of calm and safety after trauma. Dr Porges suggests that when people feel safe, they are in the social engagement state, allowing them to feel more connected to the world around them.[3] This safety can feel physical and psychological, stimulating the parasympathetic nervous system and reducing heart rate and stress hormones while fostering emotions including joy, connection, and security.

There are several ways to help to regulate the nervous system and find the ventral vagal state, including:

  • Exploring triggers – when people know their triggers they can begin to explore them and understand why they react to them in specific ways. While some triggers can be avoided, others may be more common, so identifying them and exploring responses can help people devise a plan for how they will begin to manage them in the future.
  • Bringing awareness to the body – by using techniques to bring attention back to the body, people can learn more about their physiological changes in response to stress or triggers and manage these responses more effectively. Techniques to foster more body awareness include mindful breathing, body scans, and grounding exercises.
  • Seeking safe relationships – social engagement is incredibly important for all humans. Cultivating relationships where people feel loved and supported can help them feel safer and activate the social engagement system.

Even when working with the ventral side of the vagus nerve, it can be difficult to overcome trauma and escape the immobilisation stage. In this case, do not hesitate to seek professional help for trauma.

Polyvagal Theory provides another view into trauma, showing how connection and relationships play a big role in how people respond to and heal from traumatic experiences. Working with the ventral side of the vagus nerve can help people reenter the social engagement stage and help them to feel safe and happy, even if they have been living in a state of immobilisation for a long time.

If you have a client or know of someone struggling with trauma, reach out to us at Khiron Clinics. We believe that we can improve therapeutic outcomes and avoid misdiagnosis by providing an effective residential programme and outpatient therapies addressing trauma. Allow us to help you find the path to realistic, long-lasting recovery. For more information, call us today. UK: 020 3811 2575 (24 hours). USA: (866) 801 6184 (24 hours).


[1] Gordan R, Gwathmey JK, Xie LH. Autonomic and endocrine control of cardiovascular function. World J Cardiol. 2015;7(4):204-14. doi:10.4330/wjc.v7.i4.204

[2] “Nervous System Dysregulation – Mindhealth360”. Mindhealth360, 2022,

[3] Porges, Stephen W. “The Polyvagal Theory: New Insights Into Adaptive Reactions Of The Autonomic Nervous System”. Cleveland Clinic Journal Of Medicine, vol 76, no. 4 suppl 2, 2009, pp. S86-S90. Cleveland Clinic Journal Of Medicine, doi:10.3949/ccjm.76.s2.17. Accessed 01 June 2021.