This time, I’d like to take up Polyvagal Theory, which came up in Phase II of the Rolfing training. This is because, in considering body and mind, it provides an interesting way of thinking alongside Tonic Function (see Body and Mind (2) — Tonic Function (1) and Body and Mind (3) — Tonic Function (2)).
Previously in this column, I took up a book by Peter Levine. According to that book, when animals encounter an enemy, they take two means — to fight (Fight) or to flee (flight) — but it is known that when those two cannot be taken, they take a third means, to freeze (Freeze) (see Body and Mind (1) — The Deep Layers and Trauma). There, I also introduced that a video is available (MUST SEE: How to Discharge Trauma: Trauma Release Seen For the First Time -) of a bear shot by a human with a rifle, freezing as it releases the energy produced by that shock.
In fact, the sympathetic nerve of the autonomic nervous system is involved in Fight/Flight.
The human body consists of:
the somatic nervous system, which “can be moved by conscious will,”
and
the autonomic nervous system, which “cannot be controlled by conscious will.”
And the autonomic nervous system has two antagonistic nerve systems. The sympathetic nervous system, which becomes dominant when exercising, and the parasympathetic nervous system, which works in the opposite way and becomes dominant at rest.
What is involved with Freeze, the third means, is the vagus nerve (Vagus).
The vagus nerve is the only nerve that reaches from the brain to the abdomen, exiting from the head, and it is involved in the working of the gastrointestinal tract, the bronchi, the heart, and the viscera. What is involved with freezing is, among the vagus nerve, the nerve without a myelin sheath (in the body, it is located dorsally: the Dorsal Vagus Nerve), also said to be an old vagus nerve developed since the era of vertebrates and reptiles.
In fact, Professor Stephen Porges of the University of Illinois says that mammals, including humans, developed another kind of vagus nerve. Mammals have a vagus nerve with a myelin sheath* (a new vagus nerve; in the body, located ventrally: the Ventral Vagus Nerve). This developed so as to connect to the cranial nerves that control facial expression and vocalization.
From the fact that there are multiple (two: the “old vagus nerve” and the “new vagus nerve”) vagus nerves (Vagus) in this way, Professor Porges called his idea by the name Polyvagal Theory (Poly = many, Vagal = vagus nerve).
Mammals (unlike reptiles) need to give milk when they bear young. There, a necessity arose to newly develop means of communication. For example, expressing the face with expression, crying, vocalizing, or sucking with the mouth. In particular, expressing the face with expression became an aid to bringing the sense of distance in human relationships closer. And that also connects to the way of taking distance from society (sociality).
That expression of the face, it is said, developed the new vagus nerve. As a result, through the working of the new vagus nerve, which concentrates on the face, a signal that it is all right to come psychologically closer developed. In this way, the human being came to judge, when approaching others, by the face, vocalization, and signals from others.
According to Professor Porges, the three nerve systems — the new vagus nerve (involved in psychological distance and sociality), the sympathetic nerve (involved in Fight/Flight), and the old vagus nerve (involved in Freeze) — take a hierarchical structure. That is, the new vagus nerve suppresses the lower two (the sympathetic nerve and the old vagus nerve). And the sympathetic nerve suppresses the old vagus nerve. The higher up the hierarchy, the more the sense of security increases, so the human being tries to use the topmost, new vagus nerve.
Turning it around, when an event occurs and safety is felt, the new vagus nerve works; but when a critical situation arrives, the next one, the sympathetic nerve, works, and Fight/Flight is activated. Ultimately, when a situation critical to life arrives, in the end the old vagus nerve works, and behavior called Freeze comes out.
What is interesting is that, when stress is felt, the human being unconsciously begins to use the facial muscles. That appears as behavior such as eating and drinking, listening to music, and talking with people. All of these can be thought of as behaviors, through working the facial muscles, to make the new vagus nerve dominant. Professor Porges says that, like yoga’s Pranayama (breathing method), deepening the breath connects to using the facial muscles, and that this is likewise a behavior to make the new vagus nerve dominant.
Professor Porges says that, considering that patients with autism, trauma, depression, and schizophrenia are, so to speak, in a state in which the new vagus nerve is not working, the challenge becomes how to make dominant a nerve system involved in sociality. Next time, I’d like to touch on Polyvagal Theory from this viewpoint.
*Reference: The presence or absence of a myelin sheath greatly affects the information transmission of the nerve cell. When there is a myelin sheath, it is called saltatory conduction, and the information transmission of the nerve is done rapidly; whereas when there is no myelin sheath, the information transmission of the nerve is slow.