What’s the Fuss with the Vagus?

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Well…

The vagal nerve fibers are up to 85% sensing or perceiving, in nerve speak this is termed afferent. There is a much lower concentration of motor neurons, termed efferent.

Thus, the nerve with arguably the most connection with our body is mostly sensing - this upends a lot of assumptions about nerves and the nervous system. There is a cognitive bias that our bodies are “top down,” the brain is in charge and directs function and action to the body. Not true. They are in an inter-relationship that is rooted in the body. The vagal system is a profound expression of this reality. 

What if we saw all of the endings of the vagus nerve as sense organs, how would our view of the body’s intelligence shift? It’s not literally true but it may be more true than focusing so much on the brain…

The polyvagal theory in a nutshell:

The Polyvagal Theory is a neuro-psycho-physiological theory. One way to describe the polyvagal theory is as describing a physiology of feelings and our inborn orientation towards connection with others. 

It’s exciting because it can help us and the folks we work with understand the sometimes mystifying ways we experience our own bodies. Stephen Porges is neurophysiologist and he produced some research indicating that there are two nerve nuclei in the brain that produce distinct vagus nerve tracts; the dorsal (towards the back) vagus and the ventral (towards the front) vagus (see Gil Hedley for a fantastic breakdown of this construct). The polyvagal theory then follows these nerve tracts to their linked sites in the body. The theory says that the dorsal vagal tract is evolutionarily older and we share it with our reptilian kin. The ventral vagus is evolutionarily more recent and is shared with all mammals. 

Vagus means “wanderer and in this instance refers to the sheer number of linked sites in the body the vagal system is connected to. In the sections below I will break down the two nerve tracts and in the process we will be able to understand how this system comes into play with our work. We are able to do meaningful hands-on work with many of the sites that are linked to the vagus nerve. These sites (often internal organs, facial and throat muscles and sense organs) can be considered as loci for how we sense and express our feeling states, both to ourselves (interoception) and others. 

Vagus Nerve or Vagal System? 

I prefer to think about the vagal system more than the vagus nerve itself. The vagus nerve is a pathway for information. Often, when people are referring to the vagus nerve they are really meaning the information that is moving through the vagal system. When we start to consider the system we are invited into the body’s experiential world, much of the vagal system is sensing, the nerve isn’t really the sensor, the target tissue structures are the sensor. The nerve is the conveyor of what is being sensed. 

When we shift our focus away from the nerve and towards the whole system I think we are invited into the richness of embodied experience. I’m not saying the nerve isn’t relevant, it absolutely is, but to focus only on the nerve misses other stories the body wants to tell.

Let’s look at this storying body….

Embodied Vagal System Breakdown

We can think of the vagal system as having two aspects:

  • Supradiaphragmatic - above the diaphragm: this then can be broken up into a few areas that are helpful to name and discuss:

    • Heart and lungs

    • Throat: breathing, swallowing and vocalizing

    • Sense organs of the face, especially the ears and some muscles of facial expression. 

  • Subdiaphragmatic - below the diaphragm: here we are thinking about:

    • digestion

    • elimination

    • sexual function and reproduction

Supradiaphragmatic Vagal System

This is the evolutionarily more recent aspect of the vagal system. We share this in common with our mammalian kin. This aspect of the system is related with our innate drive towards relationship and social connection. It is where we open our heart to others, use sound to both express and interpret others, view the faces of those around us and use our face to express our innermost self, take in the physicality of the world through our senses, especially through food.

This is a theory about our deeply intertwined physical relationships with our surroundings.

Heart and Lungs

These two organs can be primed towards increasing their activity and mobilizing our system if the neuroceptive system interprets something as threatening or over stimulating. This often takes the form of elevated heart rate, increased respiratory rates, tightening in the chest, etc… Based on our personal history we will have our own specific associations or interpretations of this internal state and often interpret our present situation based on these historical experiences. 

When this part of the system has been in prolonged states of stress these tendencies become patterns and even create a feedback loop where the system is responding to its own self and further accelerating what the system is already doing. 

Clinically, incidences of arrhythmias are rising overall and increasingly in younger people. And, this area connects with the throat and mouth and I hypothesize that the increasing incidences of apneas (also occurring in younger and younger people) can, in part, be viewed as reflecting vagal system disharmony.  

With a healthy vagal tone, the heart is regulating the rest of the body with its profound electrical field, the chest is relaxed and feels open, breath feels spacious and full and we are available for connection both with ourselves and others.

Throat

This is where it gets really interesting.This area involves the muscles of swallowing, breathing, vocalizing and even intimate activities such as tasting and kissing. I am seeing so many folks coming into the clinic with symptoms in this area. This is linked with breath, digestion and vocal expression. 

There is often a relationship between this part of the vagal system and the diaphragm itself. The diaphragm is mainly associated with the phrenic nerve BUT there is direct contact between the heart (via the pericardium) and the diaphragm AND the vagus nerve esophageal hiatus and plays a major role in the lower esophagus being able to coordinate itself with the muscle fibers of the diaphragm and the upper stomach - this is a dynamic transition zone. (1) 

What presents clinically is some version of up/down dysregulation that can involve:

  • Speaking: a person can have difficulty coordinating breath and speech and struggle, in certain situations, to get words out, or even feel somewhat stuck and unable to speak.

  • Breathing: breathing becomes dysregulated and uncoordinated. This will often be in specific scenarios. 

  • Upper stomach - Lower esophageal digestive issues: the esophageal hiatus or even the esophagus itself struggles to coordinate its muscular movements to support digestion. Swallowing can also become dysregulated for some folks. 

Sense Organs of the Face and Facial Muscles

The supradiaphragmatic vagus nerve has origins in both the brain stem (nucleus ambiguus) and the nuclei of the trigeminal and facial nerves, so these areas are part of the vagal system. 

This aspect of the vagal system is bi-directional and profoundly integrated with the neuroceptive system. Our neuroceptive system is cued from the womb to use our sense organs to perceive and interpret our surroundings. We look and listen and if those are unavailable seek to touch our environment in order to understand how we want to engage with it. 

If we are able to see, we are highly attuned to facial expressions; what are the eyes saying, the turn of the mouth, the brow, all of these things we are evaluating below the level of conscious awareness and responding to without thought. The same goes for tones of voice and other aspects of our sound environment if we are able to hear. 

The interesting thing here is that we use our facial muscles and sense organs both to perceive, i.e. what are the facial expressions or tones of voice being used and also we use this area to express ourselves. Both are often being engaged below the levels of our consciousness awareness. 

Porges describes this aspect of the system like this;

…through the process of evolution, the brainstem nuclei that regulate the myelinated vagus became integrated with the nuclei that regulate the muscles of the face and head. This link results in the bidirectional coupling between spontaneous social engagement behaviors and bodily states. Specifically, an integrated social engagement system emerged in mammals when the neural regulation of visceral states that promote growth and restoration (via the myelinated vagus) was linked neuroanatomically and neurophysiologically with the neural regulation of the muscles controlling eye gaze, facial expression, listening, and prosody. (2)

The Subdiaphragmatic Vagal System

80-85% of the subdiaphragmatic vagal system is afferent, meaning sensing. It is perceiving the state of the organ and communicating that back to the brain. I think we all are familiar with the sometimes immediate sensation in our gut when we are experiencing emotions. Sometimes, this “gut feeling” and our emotional awareness are in tune. However, other times, our subdiaphragmatic system is “feeling” something that our cognitive sense isn’t aware of and the physiological sensation is good at getting our attention. 

For example: many of us become habituated and adjusted to certain states of anxiety, it’s not a bad adaptation when we need to attend to all of our responsibilities, we may adapt so well that we are no longer aware of the anxiety we are carrying. But, our body lets us know maybe with some dysregulation at the esophageal hiatus which we might experience as acid reflux or feeling full and bloated without eating much, etc… 

Our physiology is in a state of what I like to call mutual-simultaneity with our emotional experience; meaning, that there is not a linear progression from an emotional feeling to physiological expression of that feeling, they happen at the same time, the western-european mind struggles with most concepts that step outside of linearity, but it’s a fact in living systems. 

Physiology is in an adaptive relationship with all of our survival strategies. In the example above, suppressing awareness of anxiety is a survival skill, it’s doing the best it can based on a lifetime of experience. Our physiology can be carrying some of the burden of how we learned to adapt to challenging circumstances and this can influence the subdiaphragmatic vagal system in such a way that the person develops either acute or chronic symptomatology.  

When I start to explore my own internal experience and what I learn from working with patients I start to see the subdiaphragmatic vagal system as being a dynamic and integral aspect of our sensory and emotional world. It is an internally perceiving system that is highly attuned to external stimuli.  

Because the subdiaphragmatic vagal system is 80% afferent/sensing, then it is possible that we can contact the sensing organ structures and through our sensitive and listening touch, make meaningful contact with the viscera and can help them feel more relaxed, less tense. The afferent nerves then send this changed state back to the brain. Or, as Porges says: 

Changing sensory feedback (of the subdiaphragmatic vagus) has the potential to influence mental and physical health.

I think this idea has been underexplored by the medical community and our work has a meaningful role to play in working with this aspect of the vagal system. 

Endnotes:

(1)https://www.ncbi.nlm.nih.gov/books/NBK547696/#:~:text=As%20the%20vagus%20nerve%20enters,biliary%20apparatus%2C%20and%20the%20gallbladder.

(2) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3108032/