The Popular Tenth Cranial Nerve

The tenth cranial nerve, the vagus nerve, has recently gotten a lot of attention.

This is for a very good reason.

Having an optimally functioning vagus nerve is vital for many critical functions in the body. It directly influences the heart, digestion, brain, and lungs.

This “vagrant”, or wandering nerve predominately guides the “rest and digest” part of the autonomic nervous system (ANS), the parasympathetic nervous system (PNS). Therefore, an optimally functioning vagus nerve allows the body to replenish, repair, and perform its subconscious functions with ease. In contrast, a heightened sympathetic nervous system (SNS) keeps the body on guard and ready to “fight and flee.”

Triggers such as stress, digestive issues, trauma, pain, heat, and other factors can cause a vagal response. This stimulation to the vagus nerve can lead to symptoms and an imbalance in the nervous system. The vagus nerve can also become damaged, leading to various disorders that impair essential autonomic functions.

Thankfully, lifestyle practices such as diet, movement, mindfulness, social connection, and music therapy can help to optimize our vagal tone and enhance our resilience. We can indirectly assess how well toned our vagus nerve is based on the fluctuations of our HRV (Heart Rate Variability) and by the symptoms we are experiencing.

In this post, I’ll explore how a theory based on the vagus nerve’s functions provides an innovative approach to dealing with PTSD (post-traumatic stress disorder). It is referred to as the polyvagal theory. I’ll also touch on how essential oils can support this therapeutic application.

The Polyvagal Theory

The polyvagal theory was introduced in 1994 by Stephen Porges. It is based on the role that the vagus nerve has in regulating emotions, social connection, and the response to fear. Today, this theory provides a new understanding for trauma. (R, R, R, R, R, R)

The polyvagal theory is defined as the scientific study that explores the neurological, psychological, and physiological responses of the nervous system to threats and safety. When one feels safe there is a downregulation of the SNS and dominance of the PNS. This allows the mind-body to be nourished and remain in balance (homeostasis) to support growth, health, and restoration. This form of regulation is the result of the bidirectional communication between our brainstem and peripheral organs via the vagus nerve. In this state of healthy adaptation we feel able to enter into constructive social relationships. These connections further buffer us from threats and optimize our vagal tone. (R, R)

As Stephen Porges wrote in a 2022 article in Frontiers in Integrative Neuroscience:

Polyvagal Theory provides an innovative scientific perspective to study feelings of safety that incorporates an understanding of neuroanatomy and neurophysiology.

This perspective identifies neural circuits that downregulate neural regulation of threat reactions and functionally neutralize defensive strategies via neural circuits communicating cues of safety that enable feelings of safety to support interpersonal accessibility and homeostatic functions.

Basically, when humans feel safe, their nervous systems support the homeostatic functions of health, growth, and restoration, while they simultaneously become accessible to others without feeling or expressing threat and vulnerability.

Feelings of safety reflect a core fundamental process that has enabled humans to survive through the opportunistic features of trusting social engagements that have co-regulatory capacities to mitigate metabolically costly defense reactions…

From a Polyvagal perspective it may be helpful to investigate how challenges move us into physiological states of threat that would disrupt our connectedness and place our mental and physical health at risk.

But, more relevant to both to clients and personal survival, therapists need to identify and emphasize the innate resources their clients have available to mitigate the potentially devasting reactions to threat, which in turn can destabilize the autonomic nervous system, sometimes resulting in visceral organ dysfunction and compromised mental health.

Clinical applications of this theory were recently adapted by Deb Dana and are found within her therapy books. She applies the concepts by Porges and its three key principles of hierarchy, neuroception, and co-regulation into therapeutic exercises. (R, R) These principles are explained as follows:

Hierarchy relates to three nervous system states:

• ventral vagal– the state of safety, we can show up, communicate, and connect with others
• sympathetic – the fight or flight energy state that is mobilized for survival in dangerous situations
• dorsal vagal – a collapsed, shut-down, numb state initiated for protection

Neuroception is the term used to refer to how our nervous system scans the environment for safety or danger, which determines our hierarchy.

Co-regulation is the biological drive to connect with others, our tribes, to survive. This persists throughout our lives.

These principles can help explain trauma and emotional patterns based on one’s state in the nervous system hierarchy.  For example, those who appear stuck or “frozen” in dysfunctional relationships are likely in a dorsal state. Whereas anxiety from trauma could likely mean one is in a sympathetic state.

The Polyvagal Theory and PTSD

When a traumatic experience occurs, the PNS is overridden by the SNS as a protective mode. This is an adaptive response in acutely dangerous and life-threatening situations; however, in the long-term it can lead to disorders. For example, if one is in a safe environment but their nervous system remains in a state of chronic fight-or-flight, significant hypervigilant psychosocial distress and poor health outcomes can result. An example of this is post-traumatic stress disorder (PTSD), a maladaptive, debilitating neuropsychiatric condition that involves the dysregulation of normal fear processes.

Clinical applications of the polyvagal theory for PTSD focus on one’s autonomic state, or hierarchy, as the mediator of mental and physical health. By helping one return to a ventral vagal state, one can shift from a neurophysiological state of disconnect to a healed, reconnective state of homeostasis in the body. This allows for more connections and healthier social relationships.

Vagal nerve stimulation and meditative practices are interventions that have been studied based on the polyvagal theory.

According to IFM:

“Studies suggest that contemplative practices, characterized by the attentive regulation of breathing, may activate the vagus nerve and increase RSA (respiratory sinus arrhythmia) that, according to the polyvagal theory, reflects the activation of the ventral vagal complex (VVC) and may promote PTSD recovery.”

It’s important to note that there is still some controversary about applying this theory based on lack of agreement on the vagus nerve’s influence on the physiology and psychology of PTSD. As stated in Psychology Today, “there is no clear consensus among biologists that the dorsal brainstorm or dorsal-ventral centers are responsible for parasympathetic control of heart rate during psychological dissociation.”

Essential Oils and the Vagus Nerve

Essential oils and aromatherapy are known to induce relaxation, calm the mind and body, and enhance mood. Along with the psychological effects, our biochemistry, neurological signaling, brain patterning, and physiology are also impacted.

By calming autonomic arousal, they can directly impact vagal tone. They combine perfectly with the holistic mental health support that naturopathic and functional medicine doctors can provide.

In future articles, I’ll dive deeper into how essential oils support the vagus nerve and which specific essential oils may be of particular benefit.

Summary of the Vagus Nerve, Polyvagal Theory, and Holistic Interventions for Trauma

The vagus nerve is the key regulator of our PNS, which sets the autonomic, subconscious processes in our body critical for our everyday functioning. When we are in a calm state our PNS is dominant, and our minds and body can heal and optimally function. However, with heightened stress and stimulation, such as from past trauma, our sympathetic nervous system overrides our PNS, and our vagal tone can become dysregulated. This can make our nervous system maladaptive and negatively impact our health, psychology, and social relationships.

The Polyvagal theory is the scientific study of the neurological, psychological, and physiological effects of feeling safe. When one is free of threat, the nervous system can relax and support mind-body balance (homeostasis) to optimize growth, health, and restoration. Mindfulness, vagal nerve stimulation, and essential oils can be used as clinical applications to calm the vagus nerve and assist one in healing from trauma.

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References:

1. https://www.uptodate.com/contents/syncope-fainting-beyond-the-basics
2. https://drruscio.com/vagal-tone/
3. https://drjockers.com/vagal-tone/
4. https://drjockers.com/limbic-retraining/
5. https://pubmed.ncbi.nlm.nih.gov/17049418/
6. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1868418/
7. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9216697/
8. https://pubmed.ncbi.nlm.nih.gov/35941799/
9. https://pubmed.ncbi.nlm.nih.gov/30953358/
10. https://www.polyvagalinstitute.org/whatispolyvagaltheory
11. https://pubmed.ncbi.nlm.nih.gov/27010234/
12. https://www.nature.com/articles/s41582-022-00635-8
13. https://www.frontiersin.org/articles/10.3389/fpsyg.2014.01571/full
14. https://www.ifm.org/news-insights/understanding-ptsd-from-a-polyvagal-perspective/