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December 26, 2018 - January 26, 2019
we can afford to be immobilized without fear (relaxed). We can maintain a vibrant tone without being collapsed or overly aroused.
Sometimes the ventral vagus is called the “new vagus” because it is more recent in terms of its appearance in our phylogenetic species history than the dorsal vagus. The ventral branch is newer in terms of evolution; it is found only in mammals, and in no other class of vertebrates,
When we (or other mammals) are safe in our environment—free from threats, danger, and unnecessary worries—and in good physical health, we normally exhibit behavior that is socially engaged.
When we are threatened or in danger, however, our autonomic ner-vous system shuts down the activity of the ventral branch of the vagus nerve and regresses to an earlier, more primitive evolutionary response of either spinal sympathetic activity (flight/fight) or depressive behavior (withdrawal).
socially engaged, we might naturally meet a new situation with openness, trust, and positive expectations.
if this prosocial behavior is not enough to neutralize the threat or danger, our evolutionarily most recent neural mechanism—the social engagement circuit—is the first to be abandoned.
If our autonomic nervous system feels that a situation is unsafe, our response can shift down one phylum, from social engagement to the level of reptiles with a strong spinal sympathetic chain response, and we might fight to overcome the threat, or flee to avoid it. If the situation is so extreme that fighting or fleeing is not enough, we may shift down even further and shut down or collapse into a dorsal vagal state of withdrawal, dissociation, and shutdown.
The dorsal branch is the older of the two branches of the vagus nerve, and is present in all classes of vertebrates, from boneless fish up to and including human beings and other mammals. It is sometimes referred to as the “old vagus.”
The hibernation of mammals involves some degree of dorsal vagal activity, but it is not the same as shutdown.
By contrast, reptiles can shutdown almost totally, reducing their heart rate, breathing, and digestion drastically to conserve energy until their next meal.
This immobilization with fear can be used as a defensive strategy, as in behaviors such as freezing and feigning death. For example, a mouse freezes when it senses a predator nearby, becoming “as still as a mouse” to avoid detection.
The Polyvagal Theory describes how a surge in the activity of the dorsal branch of the vagus nerve is a defensive strategy that causes a physi-ological state of shock or shutdown to help us cope with traumatic events, extreme danger, or imminent destruction, whether real or imagined, by suddenly collapsing and shutting down.
Unfortunately, we have remained largely unaware that another danger to our health arises from the widespread condition of chronic activation of the dorsal vagus circuit.
When dorsal vagal activity is less extreme but chronic, its emotional correlate is characterized by depressive feelings.
People with a diagnosis of depression, or people in a depressed state, typically lose interest in activities that once were pleasurable. They over-eat, experience loss of appetite, or have digestive problems. They have reduced energy, and they become inactive, introverted, apathetic, help-less, and asocial.
When a person faces an overwhelmingly dangerous situation and/or the possibility of imminent death, it is a natural reaction to dissociate from one’s own body, from the here and now; to shut down physically, emotionally, and mentally;
He describes what he calls the “vagal brake”—how activation of the social engagement circuit “puts the brakes on” the other circuits and lifts us out of a chronic dorsal vagal or spinal sympathetic state.
Under normal conditions of challenges to survival, the spinal sympath-etic chain or the dorsal branch of the vagal nerve may be triggered into active states of defense. However, when social engagement is coupled with either of these circuits, the range of human behavior is expanded by keeping the individual out of a defensive state.
Using the exercises in this book, it should only take a minute or two to get back into a state of social engagement.
The other response comes from activation of the dorsal vagal circuit: Our muscles and connective tissues lose their normal tonus, soften, and go limp, and our body feels heavy. To someone else, our muscles feel flac-cid. If we try to do even a small task, it takes a monumental effort to move.
the blood withdraws from the periphery of the body and gathers in the center.
Thus our hands and feet feel cold and clammy.
Rather than simply massaging an area that hurts, the best way to treat this condition is to elevate the person from a dorsal vagal state by activating the ventral circuit state,
a state of shock or shutdown: The face loses its color and appears lifeless and unre-sponsive; the facial expression is unchanging and facial muscles sag.
The voice also lacks prosody (melodic expressiveness); it is flat and without melody. The eyes appear dull and lifeless—there is no sparkle. We may also have low blood pressure,
This occurs because, if our muscles are undertoned, our blood pressure does not need to be high in order to push blood through th...
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Our mental awareness turns inward, or even disappears entirely when overwhelming danger presents itself, resulting in dissociation, a withdrawal of consciousness from the body.
We are not in the here and now, and we may feel as if we are hav-ing an out-of-body experience, as if watching what is going on from a great distance.
The blood flow to the frontal lobes of our brain is also reduced by dorsal vagus activation. These lobes are where our higher functions reside; the frontal lobes are considered the human part of the brain and are involved with the functions of language and will. By “will,” I mean conce...
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Dissociation is a widespread problem. It can be characterized as ongoing activity of the dorsal vagus nerve that keeps us in a physiological state of fear.
We may be present in a group but not take part in a conversation; we may be lethargic and lack empathy.
(Note that modern reptiles are not the evolutionary ancestors of mammals; primitive, now-extinct reptiles are our evolutionary precursors.)
In the entire animal kingdom, only mammals have a ventral circuit,
The brainstem extends from the brain; it lies on the underside of the brain and is the beginning of the spinal cord. Cranial nerves, except for cranial nerves I (olfactory) and II (optic), originate in the brainstem. The vertebral artery supplies blood to the brainstem and the five cranial nerves.
The two divisions of the vagus nerve each go to the heart, the lungs, and the airways. In addition to this, the ventral vagus branch extends to the muscles of the throat (larynx and pharynx), and it relates to movements of the face.
In addition to reaching the heart and lungs, the dorsal vagus nerve branch goes to the subdiaphragmatic organs of digestion (except for the descending colon). It goes to the stomach, liver, pancreas, spleen, ascending colon, and transverse colon.
All of the twelve cranial nerves originate on the inferior (bottom) surface of the brain or from the brainstem. We are especially interested in CN V, VII, IX, X, and XI. All five of these nerves need to function properly if we are to be socially engaged.
The eleventh cranial nerve (CN XI), one of the five nerves necessary for social engagement, also innervates the trapezius and sternocleidomastoid muscles.
Working together, the trapezius and sternocleidomastoid muscles allow us to move our head precisely, to position our eyes, ears, and nostrils to get important information from our environment.
When a baby is lying on its stomach, one of the first movements it makes is to lift its head. To do this, it tenses all three parts of its trapezius muscle. Tightening the fibers of its upper trapezius tips its head back and up. Tightening its middle trapezius pulls its shoulder blades together and stabilizes its arms so that they can support the weight of its body. Tightening the lower trapezius allows it to arch the entire length of the spine.
When the baby comes up on its hands and feet to crawl, the three parts of the upper, middle, and lower trapezius muscles continue to tighten in the same way as when it lay on its stomach and lifted its head.
A forward head posture comes from an upper trapezius that is not too tight but too flaccid. As years pass, the upper trapezius becomes even more and more slack, and the head slides increasingly forward on C1.
The Twist and Turn trapezius exercise in Part Two of this book helps to bring the head back into better alignment because it stimulates all three parts of the muscle.
Spontaneous changes of facial expression, especially when someone is looking directly at another person, are a sign of social engagement. These small changes occur at a rate of several times per second. The individual expressions are too fast to notice, but we can see that there is life in the face. When someone is socially engaged, the spontaneous facial movements occur in the zone between a line drawn across the middle part of the eyes and a line between her lips.
