Lois’ Notes: The Vagus nerve controls our fight-or-flight response, and it can be modulated by deep breathing. Treatment for PTSD? Meditation? Indeed, yes. All the above.

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Have you ever read something a million times only to one day, for no apparent reason, think “Wait, what is that?” This happened to me the other day for “the vagus nerve.”

I kept coming across it in relation to deep breathing and mental calmness: “Breathing deeply,” Katie Brindle writes in her new book Yang Sheng: The Art of Chinese Self-Healing, “immediately relaxes the body because it stimulates the vagus nerve, which runs from the neck to the abdomen and is in charge of turning off the ‘fight or flight’ reflex.” Also: “Stimulating the vagus nerve,” per a recent Harvard Health blog post, “activates your relaxation response, reducing your heart rate and blood pressure.” And: Deep breathing “turns on the vagus nerve enough that it acts as a brake on the stress response,” as an integrative medicine researcher told the Cut last year.

I liked this idea that we have something like a secret piano key, under our skin, to press internally to calm us down. Or like a musical string to pluck. At this point I was envisioning the vagus nerve as a single inner cord, stretching from the head to the stomach. In reality, the vagus nerve is a squiggly, shaggy, branching nerve connecting most of the major organs between the brain and colon, like a system of roots or cables. It is the longest nerve in the body, and technically it comes as a pair of two vagus nerves, one for the right side of the body and one for the left. It’s called “vagus” because it wanders, like a vagrant, among the organs. The vagus nerve has been described as “largely responsible for the mind-body connection,” for its role as a mediator between thinking and feeling, and I’m tempted to think of it as something like a physical manifestation of the soul. Also: “When people say ‘trust your gut,’” as one Psychology Today writer put it several years ago, “they really mean ‘trust your vagus nerve.’”

I became increasingly enchanted with this nerve, even as it felt like I understood it less and less. How does this all work? How does activating a nerve calm us down? Is this why I get so needlessly upset about things?

“Stimulating the vagus nerve to the heart has a really powerful effect on slowing the heart rate,” said Lucy Norcliffe-Kaufmann, associate professor of neurology at NYU-Langone. And this, specifically, is what relaxes us. The vagus nerve is basically listening to the way we breathe, and it sends the brain and the heart whatever message our breath indicates. Breathing slowly, for instance, reduces the oxygen demands of the heart muscle (the myocardium), and our heart rate drops.

The vagus nerve is essentially the queen of the parasympathetic nervous system — a.k.a. the “rest and digest,” or the “chill out” one — so the more we do things that “stimulate” or activate it, like deep breathing, the more we banish the effects of the sympathetic nervous system — a.k.a. the “fight or flight,” or the “do something!” stress-releasing adrenaline/cortisol one.

Put another way, “Your body senses your breathing and adapts its heart rate  READ MORE