An Update on the Autonomic Nervous System

Feb 01, 2019
How the Autonomic Nervous System (ANS) works

Summary of the Polyvagal Theory by Stephen Porges and it's relevance to ME/CFS, FM and ES

What is the Autonomic Nervous System and how does it work?

The autonomic nervous system (ANS), which functions involuntarily below the level of consciousness, is the part of our nervous system (nerves, spinal cord and brain) which involuntarily and below the level of consciousness keeps our body in homeostasis and responds to threats. For many decades we have considered the ANS to have two components: the sympathetic nervous system which readies us for fight or flight in the case of danger (fight/flight) and the parasympathetic nervous system which helps us recover and grow (rest & digest). I discuss this traditional model of the ANS on pages 3-16 – 3-24 of my manual "Let Your Light Shine Through". The freeze response is left out of this discussion.

It is widely believed that chronic conditions are caused by or influenced by chronic stress. The theory is that chronic stress keeps the fight/flight system activated. This results in too much cortisol and adrenaline and shuts down the adaptive and growth systems in the body (rest/digest). Heart Rate Variability (HRV) is a way to measure ANS function. My HRV research in individuals with ME/CFS, FM and ES did not show this. Rather than showing an overactive fight/flight system, I found that the rest & digest system is underactive. I have been seeking an explanation for my research findings.

It turns out that the traditional 2 part model of the ANS is incomplete. Dr. Stephen Porges is a senior researcher who has spent the last 35 years studying the ANS. He has written several books, most of which are collections of scientific papers and not very easy to understand. In 2017, Porges wrote, “The Pocket Guide to The Polyvagal Theory” which is a series of interviews. Although still quite heavy going, this small book gives hints about how to improve chronic health and mental health symptoms. This newsletter is a summary of Porges’ Polyvagal Theory.

The ANS has Three Parts (not two)

1. Fight/Flight

The ANS is constantly evaluating risk and safety. Danger cues such as low-frequency noises, aggression or lack of face-to-face engagement may trigger the sympathetic fight/flight system. A person may have a racing heart, breath faster, feel tight, sweaty and have abdominal pain. All of this happens outside our awareness and control. However, our conscious brain tries to make sense of experience. When we feel unsafe, we develop a story to explain why are reacting. Our stories may or may not be accurate. For example, a person who is depressed may notice bodily sensations and create a story that justifies their urge to remain isolated for the sake of safety. A different story might lead to different behaviour. Without questioning our stories, we can continue in a behavioural rut that doesn’t serve our best interests.

2. Freeze

Lethal situations in which there is no hope of escape can trigger the old reptilian parasympathetic freeze system. This is found in most living creatures (reptiles, fish, birds and mammals) and enables us to freeze when there seems no hope of escape. This is what happens when a lizard freezes or a mouse “plays dead” in the jaws of a cat. The mouse isn’t actually “playing”. The freeze response is an involuntary response to almost certain death. The body shuts down. Blood pressure and heart rate drop, vision go black and the brain stops working for a few seconds.

Porges suggests that the traumas that elicit a freeze response are so severe that the ANS setpoints are altered. With altered set points, the body may initiate the freeze or shut-down response when a situation is not life-threatening. Many of the symptoms of Post Traumatic Stress Disorder such as panic, dissociation and amnesia may be related to the freeze response.

I wonder if an altered set point may also be at play in people with ME/CFS who have a vasovagal syncope (pass out). Porges emphasizes that these symptoms are adaptive and involuntary reactions to a life-threatening trauma and that our executive brain has little influence. In mammals, the freeze-related symptoms will only be lessened if enough safety is created that the body can cease to feel in danger. Many successful trauma therapies now focus on body-centred, safety-enhancing approaches. Peter Levine’s “Somatic Experiencing” is one example of this. 

3. Social Engagement

Porges’ contribution to the field is recognition that for mammals, safety requires not only the absence of danger but the presence of social engagement - the non-threatening faces, sounds and gestures of others of the same species - to regulate their physiology. We cannot survive well alone. An example of social engagement is a litter of puppies or cubs that play with each other, rolling, growling, play biting but not hurting. Physical contact, face-to-face contact and vocalizations help mammals regulate their emotions and behaviour.

Porges describes a social engagement system that is hard-wired by the vagus nerve, part of the parasympathetic nervous system. This “neural pathway supports health, growth and restoration” (Porges pg100). Lest we be lulled into black and white thinking that social engagement is all good and fight/flight and freeze are all bad, there is a downside to the social engagement system. While engaged with others we are not scanning for danger and may be caught off guard. Each of us tries to find the right balance given our biology and circumstances between social engagement and danger awareness.

What does Polyvagal mean?

Polyvagal refers to the three anatomically separate parts of the vagus nerve:

  • The reptilian freeze pathway (also called the ancient or dorsal vagus)
  • The mammalian social engagement pathway (also called the mammalian or ventral vagus)
  • The 80% of vagal fibres that bring information from the environment back to the brain (the afferent vagus)

The fight/flight system is not wired by the vagus – it has its own neural pathways.

Is the Autonomic Nervous System Hierarchical?

  • First to react: When we sense danger, our mammalian social engagement system is usually the first to react. We use our faces and our voices to figure out what is going on and signal positive intent to others.
  • Next: If that doesn’t work we may become aggressive or flee (fight/flight).
  • Last resort: If none of this works and escape is impossible the ANS may shut down our bodies and minds until the danger passes (freeze).

The Autonomic Nervous System (ANS) in the Severely Ill

We know from numerous Heart Rate Variability studies (including mine) that the ANS function is not optimal in ME/CFS, FM and ES. There is some combination of under-activity of the social engagement system and over-activity of the fight/flight and freeze systems. Porges’ description of the social engagement system wired by the vagus nerve makes me wonder whether this explains my findings of severely underactive parasympathetic (vagal) tone.

I have seen severely ill patients whose ability to engage is severely affected. Their faces don’t show emotion, they lose inflection when talking. They are hypersensitive in all senses and have significant brain fog. I used to think these symptoms were due to fatigue. But maybe it is also because the social engagement vagal system has been overpowered by the over-activation of the self-protective fight/flight and freeze systems. Severely ill patients also have physical symptoms of the shutdown, the heart can be slowed, the bowels don’t work well, blood pressure becomes low and unstable.

How is Polyvagal Theory Used in Therapy?

The social engagement system has the capacity to moderate both the freeze and fight/flight systems. For example, play involves fight/flight activation moderated by social engagement. Intimacy involves freeze moderated by social engagement. Conversely, if the system is strongly in freeze or fight/flight the social engagement system may not be able to engage. These interactions between the parts of the ANS suggest that we may be able to improve health symptoms if we balance or adapt the ANS. Porges emphasizes throughout his books that because the ANS functions outside conscious awareness, cognitive strategies have limited effectiveness. Body-centred and sensory approaches are more effective. Below are some ideas.

1. Find a Safe Therapeutic Environment

Porges believes that recovering from chronic mental and physical health conditions requires the activation of the social engagement system. For this to occur, an individual must feel safe. In a doctor’s office or therapy room, Porges suggests quiet – eliminating low rumbling noises (like air circulation systems). Predictability - knowing what to expect in a therapeutic encounter increases a sense of safety as does kindness, respect and a collaborative approach.

Being judged or evaluated triggers the fight/flight system. The process of medical diagnosis is a judgement that can trigger involuntary danger responses. In being diagnosed we are being told that something is wrong with us. And it may be implied that it is our fault. When people aren’t believed by health care professionals or are repeatedly asked to prove themselves to an insurer they are thrown into a state of chronic danger.

Even if the patient uses their higher brain and consciously tries to let go of feelings of threat, the ANS is not fooled. This may be why people going through severe stressors such as divorce, financial insecurity and contested disability claims often get worse instead of better. Repeated judgements trigger the fight/flight response which impairs healing. This is an involuntary response. These patients are not trying to get worse; in fact, they may be doing everything they can to get better and are frustrated “it’s not working”.

Notice that I used the term “feeling judged”. Judgement is in the eye of the judge, not the judge. One person, because of their circumstances or past history may find a situation stressful or traumatic, while another exposed to the same interaction may not. So for patients, I recommend that if you don’t feel safe with your care providers it is worth the effort to find others with whom you feel safe. If I find myself judging a patient, I have likely just ruined their sense of safety and their ability to benefit from the interaction; very humbling.

2. Listen to your Body

If we pay attention to how our body (influenced by the ANS) feels, we can observe which situations put us into a fight/flight or freeze state and which allow us to flourish – interact, be creative, learn and remember etc. When we feel safe we have access to more of our emotional and cognitive functions. When we feel in danger our focus is narrowed to self-protection.

The process of self-observation and charting that we experience in the Psychoeducational Group is based on this premise. If you observe your body and learn its patterns, you develop trust in your body and your ability to meet your own needs. Some of our interpretations will be incorrect – it’s very hard to accurately figure out what the ANS is doing and why. But we will be farther ahead than if we dismiss the body signals as unimportant. Symptoms are the body’s way of letting us know what it needs. They have a useful purpose.

Mindfulness is a useful tool for body awareness.

Pause your day.

Focus your attention on your breath.

Notice what arises in your body.

3. Use your Sound and Voice

Listening to music and human voices which have lots of variability of tone stimulates the social engagement system. Singing involves many activities which increase the social engagement system. Slowed breathing activates the vagus nerve. Singing requires controlling the breath and slowed outbreaths. This leads to a calmer physiologic state as measured by Heart Rate Variability. Singing also involves controlling the muscles of the throat. Listening to human voice/s increases control over the middle ear and the ability to distinguish and understand voices. If you are singing with others then you are also getting social cues from the voices and faces of others and this strengthens the positive impact. Porges compares this positive face to face activity with the far more common but less effective social engagement with objects such as computer games or smart phones. His theory suggests that joining a singing group can be very therapeutic. This assumes that participants’ voices or participation are not being judged.

4. Safe and Sound Protocol®

Dr. Porges has developed a program called the Safe and Sound Protocol® which involves listening to music that has been processed to stimulate the “social engagement” system. In as little as 5 X1 hour sessions, improvements have been reported in children with autism, Attention Deficit Disorder and trauma history.  After the treatment, these children have improved their ability to interpret human speech and interpersonal interactions improve.

Porges also reports positive clinical experience with people who have auditory hypersensitivity secondary to conditions such as autism. I wonder if this modulated music would help people with ME/CFS and ES who have auditory hypersensitivity. A study is currently underway in older adults with chronic pain – presumably, this study is assessing whether activating the social engagement system can calm the nervous system and lessen chronic pain.

5. Calm the Mind and Body

Heartmath® is a Heart Rate Variability biofeedback app designed to improve ANS balance. By regulating breathing while focusing on positive thoughts and emotions, one can “better manage life’s challenges, improve overall health, emotional wellness and resilience”. (quote from AHS  Heartmath® information). AHS offers free Heartmath® training often at the South Health Campus. 

Heartmath is only one of many strategies to improve ANS function. Each person is different. Choose a strategy that appeals to you, one that you will look forward to practicing daily. Mindfulness meditation, breathing, singing, walking in nature, yoga, qi gong and others are also great choices. Most of the patients I have observed getting better have taken their ANS function seriously.


Porges’ polyvagal hypothesis may provide new insight into a contributor to chronic conditions. The ANS has three physically and behaviorally distinct functions, all with the goal of protecting life (freeze), responding to danger (fight/flight) maintaining homeostasis in the body (all) and enhancing emotional and behavioral stability (social engagement).

Mammals prosper when these parts of the ANS are incoherent balance. Porges’ research suggests some ways to survive and thrive even in the face of adversity or after surviving trauma.

Author: Eleanor (Ellie) Stein MD FRCP(C)

I am a psychiatrist with a small private practice in Calgary and am an assistant clinical professor in the faculty of medicine at the University of Calgary. Since 2000, I have worked with over 1000 patients, all with ME/CFS, FM and ES. My passion for this field comes from my own struggle with these diseases, my desire to improve my health and then pass on what I learn. My goal is for every patient in Canada to have access to respectful, effective health care within the publicly funded system. 

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