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Polyvagal Theory 101 - a blueprint for your nervous system

Polyvagal Theory 101 - a blueprint for your nervous system

Have you ever felt like you over-react or are stressed out all the time? Understanding how the vagus nerve and Polyvagal theory work may hold the answers for how to live a calmer, more present life.

So much of the way we behave is informed by early childhood conditioning and stress responses. Far from being fixed, these responses can be adapted so that we can flexibly move from stressful situations back into a calm state. Without most of us ever knowing it, the vagus nerve informs every part of our lives – sick to your stomach, warm hearted, open hearted, gut instinct, butterflies in your stomach – these all describe feelings involving the vagus nerve. Understanding how the nervous system, the vagus nerve and Polyvagal theory work can help us to better adapt to challenges in our lives.

What is polyvagal theory in simple terms?

Stephen Porges, a professor of psychiatry and bioengineering, first put forward Polyvagal theory in 2011. The theory outlines that people have three adaptive responses – one for safety, another for danger, and the other for extreme threat to life. These responses are mediated by the vagus nerve and each is activated by what we perceive to be happening around and within us at any given moment.1

Polyvagal theory also involves the response by the autonomic nervous system (ANS) – the part of the nervous system that controls involuntary processes such as blood pressure and heart rate. The ANS is influenced by central nervous system (CNS) and responds to signals from environment, as well as the bodily organs.1

Anatomy and physiology 101: The vagus nerve and the nervous system

To better understand Polyvagal theory, we need to have a quick anatomy and physiology lesson:

The vagus nerve is the 10th cranial nerve (there are 12 altogether) and starts out at the medulla oblongata where the brain connects to the spinal cord. While it’s spoken about as being one nerve, it’s actually two that come out either side of the brain stem.2

The vagus nerve is sometimes referred to as the body’s ‘superhighway’ because of its capacity to shuttle important data to the internal organs and let the body know when it’s time to rest and digest, or fight/flee as the case may be. It’s involvement in the function and regulation of body systems is widespread – from the digestive and respiratory systems, to the heart, and all the nerves and fibres involved in the daily process of being human – from unconscious facial expressions to general wellbeing.2

Put quite simply, there’s practically no system of the body that isn’t impacted by the vagus nerve.

Neuroception is a term that Porges came up with to describe the subconscious ability that all humans have to assess whether a situation is secure, a mild threat or potentially deadly. From just one experience of an actual or perceived threat, we store these memories with the help of the amygdala – a part of the brain and limbic system which plays many important roles, including in the processing of fear, emotion and behaviour.3  Neuroception gathers information from interoception – the ability to assess the sensations in your own body – and exteroception – you guessed it, the sensitivity to stimuli surrounding the body.4

According to Polyvagal theory, there are three main branches of the vagus nerve - the ventral vagal complex, the dorsal vagal complex and the sympathetic nervous system or ‘fight or flight’ response.

Fight or flight is a life-saving defensive response that allows us to do what is necessary to get out of danger. This response involves an increase in adrenaline, blood pressure, heart rate, and a temporary decrease in immunity and digestion. In non-life threatening situations it will also show up as fear, worry, anger and frustration. 

The ventral vagal complex (“rest and digest”) is part of the parasympathetic nervous system. It controls the ability to self-regulate and feel safe so that we may socialise, emotionally connect, communicate effectively, feel compassion and empathy, and stay calm.

The dorsal vagal complex (freeze response) is a primitive response. In this state, we completely shut down. During the freeze response, the metabolism, heart rate, breathing rate and blood pressure all slow right down. Emotionally, it can feel like hopelessness, stagnation, depression, giving up, and even disassociation. The dorsal vagus nerve has a large role in controlling the lungs, heart and stomach/digestion. A shutdown response can also lead to issues with these organs.2

The HPA axis

Constant activation of the fight or flight response through stressful events can lead to something called hypothalamic-pituitary-adrenal (HPA) axis dysfunction. The stress response is mostly controlled by this axis – when stress triggers a response from the HPA axis, it results in a ‘cascade’ of hormones such as cortisol, adrenaline and noradrenaline. If this process happens repeatedly, a chronic picture of stress develops – reduced resilience, a disrupted sleep cycle, and either too much or not enough cortisol production.5

The hypothalamus, pituitary gland and adrenal glands are all responsible for the production of neurotransmitter and hormones (DHEA, melatonin, cortisol and adrenaline), so a dysfunction here can impact essentially every organ and system, such as the thyroid, reproductive system, immune system, gut and brain. 

A dysfunctional HPA axis is a condition that is at the root of so many symptoms and disorders I see in patients every day – from depression, fatigue, irregular menstrual cycles, mood swings through to insulin resistance, weight gain, and digestive disorders.

Evolution and Polyvagal theory

Porges believes that the ANS has a predictable pattern of reaction that has everything to do with our evolutionary history, from ancient reptile to mammal. Basically, we no longer needed our primitive reptilian reactions to survive in the same way. Instead, we needed social behaviours such as cooperation and caring, like mammals.2

In order to do this, over time the ANS downregulated the more defensive survival responses. A second pathway developed, known as the ventral vagal complex, that had the ability to reduce the more primitive primary defences of fight or flight and immobilisation. The ventral vagal complex only exists in mammals. It’s found to interact in the brain stem with parts of the brain that control muscles in the face and head that are responsible for helping with social engagement.2

From this evolutionary process, mammals were then able to communicate to each other, either vocally or through body language and facial expressions, that they were either safe or in danger. It was also an important pathway in helping mammals to stay connected and to co-regulate when necessary.1

Polyvagal theory and co-regulation

Co-regulation co-evolved with the appearance of the ventral vagal complex and our need for social engagement as a new means of survival. As mammals began to communicate that they were safe or in danger, this formed the basis of the need for co-regulation in social animals.6 

Co-regulation is often talked about in psychology with regards to children and trauma responses. It’s the ability, developed in childhood, of humans to soothe themselves and manage upsetting emotions. Co-regulation is learned via connection with caregivers who provide security and nurturance.

The capacity to develop co-regulation requires responses from caregivers such as:

  • Calming presence
  • Verbal affirmation of upsetting experience
  • Safe environments
  • Structure
  • Support amidst emotional arousal.6

If these co-regulation responses and safety are not met as children, it can result in a lack of capacity to self-regulate. Self-regulation is the ability to manage your own internal emotions and reactions.7 A lack of self-regulation in adolescence and adulthood can look like poor self-esteem, rigidity, difficulty managing stress, feelings of frustration, anger and anxiety.8

On the other hand, children that grow up with parents who model co-regulation develop into adults who are able to calm themselves when upset, be effective communicators, work in ways that align with their values, maintain flexibility and optimism in the face of challenges, stay focussed and take charge when needed.8

Polyvagal theory for treating trauma, anxiety and depression 

Polyvagal theory provides a blueprint for the effective treatment of trauma, post-traumatic stress disorder (PTSD), depression and anxiety. The theory gives a clear understanding for practitioners and patients alike to better understand the nervous system response that is happening in these conditions.

Mental health practitioners will often use techniques such as changing vocal patterns and facial expressions to help bring about a greater sense of safety in their patients. Breathing patterns that have a longer exhale than inhale are also used to tap into the parasympathetic branch of the nervous system.1

So many of the techniques now available not only aim to re-shape the habits of the nervous system, but also help to uncover the whole story underlying symptoms and conditions that the autonomic nervous system holds onto after a difficult event.

Check out my previous article about the simple ways to incorporate the vagus nerve into your self-care practice.

No matter what your response to a stressful event, having an understanding of Polyvagal theory and accessing the ventral vagal complex can not only help the mind and body to relax and allow for social connectedness, but also prevent damage to the nervous system. 

Book in to NEW Online Program - How to Regulate An Overwhelmed, Fearful & Anxious Nervous System - here Sign ups close on Wednesday, 27th October 2021.


  1. Porges, S.W. & Dana, D. S. Clinical Applications of the Polyvagal theory: The Emergence of Polyvagal-Informed Therapies, 2018. New York: W.W. Norton.
  2. Porges, S.W. & Buczynski, R. The Polyvagal Theory for Treating Trauma. NICABM, (n.d.).
  3. Neuroscientifically Challenged. Written June 2014, accessed October 2021 from
  4. Psychological Science. Interoception: How We Understand Our Body’s Inner Sensations. Written September 2019, accessed October 2021 from
  5. Guilliams, T.G. & Edwards, L. Chronic Stress and the HPA Axis: Clinical Assessment and Therapeutic Considerations. The Standard, 2010;9(2).
  6. Complex Trauma. Co-Regulation. Accessed October 2021 from
  7. Complex Trauma. Self-Regulation. Accessed October 2021 from
  8. Very Well Mind. How to Develop and Practice Self-Regulation. Reviewed October 2021, accessed October 2021 from,diagnosed%20as%20a%20mental%20disorder.