In 2006, I wrote a book review on “The Integrative Action of the Autonomic Nervous System–Neurobiology of Homeostasis” by Wilfrid Janig (Vol. 1 No. 6). This was a landmark textbook, an update on current research in autonomic neurophysiology and a great resource for the serious neural therapist. This month, I have another book on autonomic neurophysiology to recommend: “The Polyvagal Theory” by Stephen Porges.
Porges is a behavioral neurophysiologist and psychiatrist. This work is the culmination of 40 years of research into the relationship between autonomic neurophysiology and behavior. The word polyvagal refers to a discovery that the vagus nerve (and related cranial nerves) have two distinct, but overlapping divisions: the “vegetative vagus” and the “smart vagus”.
The “vegetative vagus” is the one we all know about – the unmyelinated fibres from the dorsal motor nucleus of the brainstem innervating the visceral organs that maintain homeostasis. It is the one most active during times of rest when the body concentrates on digestion, elimination, restoration of energy, etc. It is the primary constituent of what we call the parasympathetic nervous system.
The “smart vagus” is the new one (at least to me). As a medical student I always wondered why the vagus sent off these little branches to the ear, the oropharynx and the larynx. Now I know!
The smart vagus is actually a system of myelinated fibres from the nucleus ambiguous and the nuclei of the facial and trigeminal nerves innervating the supra-diaphragmatic organs, the muscles of facial expression and chewing, the muscles of the middle ear, the smooth muscles involved in sucking and swallowing and the larynx. Some of these branches travel through other cranial nerves including nerves 5,7,9, and 11.
The smart vagus is found only in mammals and is involved in activity required for social engagement: smiling and gestures needed for individuals to “feel safe” in social encounters, behaviours facilitating mother-infant bonding, and behaviours of courtship and male-female bonding. When the smart vagus is active it actually suppresses the sympathetic nervous system, calming the individual and allowing comfortable social interaction to take place. (The one exception is during sexual activity when both parasympathetic and sympathetic systems come to the fore.)
From a phylogenetic standpoint, this capacity for social engagement is an evolutionary achievement. When encountering danger, the most primitive organisms have only one option – to immobilize or “freeze”. The potential for this reaction is retained in all animals (including humans), but at a higher level of organization mobilization (“fight or flight”) becomes an option. This reaction has become possible through the development of the sympathetic nervous system and the adrenal medulla. Finally with the evolution of the smart vagus, a choice is available when encountering stress: (1) “fight or flight” or (2) defusing the situation through calming expressions and gestures. The second option actively suppresses the first.
The suppression of sympathetic activity can be measured through observation of the respiratory sinus arrhythmia (RSA). Smart vagus fibres act as a “brake” on the heart. Withdrawal of vagal tone increases heart rate and allows sympathetic dominance. Apparently a better measure of overall health than heart rate variability, RSA is used in monitoring high-risk newborns and also in autonomic nervous system research.
The Polyvagal Theory is a fascinating book not only for behavioural psychologists, psychiatrists and clinicians but also for anyone interested in autonomic nervous system physiology. Porges demonstrates that emotion is not just a brain thing. He shows that the internal organs are intimately connected with emotions and human behaviour (just as the Chinese have been saying for millennia!). And he makes application to vexing psychiatric conditions like autism, PTSD and borderline personality.
What has this book to offer to the neural therapist? I think understanding the polyvagal theory provides new insight into how our patients deal with stress. I have one patient recently who went into a catatonic state (a classical conversion reaction) as a result of a whiplash injury. This was an example of a primitive immobilization reaction. Similarly we all have patients who are in a sympathetically dominant “mobilization” mode. They are anxious and hard to reach, but appealing to their smart vagus can be calming: a friendly smile, low voice, slow speech and reassuring demeanour.
And then there is the subject of visceral-emotional connections. See Chapter 11 of my book (Psychological Aspects of Neural Therapy). The neural therapist has two options, (1) neural therapy of the affected organ to help the emotional state and (2) psychotherapy (perhaps using applied psychoneurobiology) to help the physical state of the organ.
Two final comments about The Polyvagal Theory: Porges includes visceral afferent fibres in his definition of the autonomic nervous system. Jänig does the opposite (and explains why!). Why is there still no consensus on this subject after 100 years?
Secondly, there is a great deal of repetition in this book. The basic ideas of the polyvagal theory and many others are restated in chapter after chapter. For the student new to the subject this is actually helpful but I found myself skipping paragraphs for sake of time. On the other hand anyone dipping into the book would be given enough background material to make sense of every chapter.
An interesting and thought-provoking book!