The mysterious nerve network that quiets pain and stress — and may defeat disease
Dec 19, 2019 · 5 min read
Take a deep breath. Hug a friend. Reach for the ceiling and stretch your limbs. Each of these simple acts bestows a sense of calm and comfort. And each works its soothing magic in part by activating a complicated system of nerves that connects the brain to the heart, the gut, the immune system, and many of the organs. That system is known collectively as the vagus nerve.
The
vagus nerve is one of the twelve cranial nerves, which sprawl out from
the brain and into the body like an intricate network of roots. These
nerve networks act as lines of communication between the brain and the
body’s many systems and organs. Some of the cranial nerves interpret
sensory information collected by the skin, eyes, or tongue. Others
control muscles or communicate with glands.
The
vagus nerve, also called the “10th cranial nerve,” is the longest,
largest, and most complex of the cranial nerves, and in some ways it’s
also the least understood. Experts have linked its activity to symptom
changes in people with migraine headaches, inflammatory bowel disease,
depression, epilepsy, arthritis, and many other common ailments. The
more science learns about the vagus nerve, the more it seems like a
better understanding of its function could unlock new doors to treating
all manner of human suffering.
Vagus
is Latin for “wandering,” which is apt when one considers all the
different parts of the body the vagus nerve reaches. “It seems like
every year somebody finds a new organ or system that it talks with,”
says Tiffany Field, PhD, director of the Touch Research Institute at the
University of Miami School of Medicine.
“There’s a massive bioelectrical and biochemical series of events that the vagus nerve is responsible for, and all that is almost impossible to map.”
Field
says that branches of the vagus nerve are connected to the face and
voice. “We know that depressed people have low vagal activity, and this
is associated with less intonation and less-active facial expressions,”
she explains. A separate branch of the vagus nerve runs down to the
gastrointestinal tract. Here, low vagal activity is associated with
slowed gastric motility, which interferes with proper digestion, she
says.
Still other branches of the vagus nerve are connected to the heart, the lungs, and the immune system. The
vagus nerve’s activation or deactivation is tied to the ebb or flow of
hormones such as cortisol and the digestive hormone ghrelin, the amount
of inflammation the immune system produces, and many other internal
processes that shape human health and experience. “There’s a
massive bioelectrical and biochemical series of events that the vagus
nerve is responsible for, and all that is almost impossible to map,”
Field says.
How
could one nerve system control so much? While some aspects of vagal
activity are inscrutable, it’s clear that the nerve is the governor of
the parasympathetic nervous system, which helps control the body’s
relaxation responses. In simple terms, heightened vagal activity
counteracts the stress response, which involves the sympathetic nervous
system. “The sympathetic nervous system is fight or flight, while the
parasympathetic nervous system is more chill out,” says Stephen
Silberstein, MD, a professor of neurology and director of the Headache
Center at Philadelphia’s Thomas Jefferson University Hospitals.
Silberstein co-wrote a comprehensive 2016 review
of the research on the vagus nerve. He says that heightened vagal
activity slows heart rate and also switches off inflammation, in part by
triggering the release of immune system calming chemicals. There’s also
evidence that activating the vagus nerve through electronic stimulation
can produce a range of health benefits. “Depending on the frequency of
the stimulation, we know it can turn off an asthma attack or an
epileptic seizure,” Silberstein says. “It can turn off a migraine or
cluster headache, and it can decrease the perception of acid reflux.”
Pick
almost any common medical condition that’s made worse by stress or
inflammation — everything from arthritis to inflammatory bowel disease —
and there’s research showing that vagus nerve stimulation can help
treat it or relieve its symptoms.
In
the past, this stimulation required a surgical implant in the chest
that transmits electrical pulses directly into the vagus nerve. But some
newer, noninvasive devices — including one that has FDA approval
for the treatment of migraine and cluster headaches — are capable of
stimulating the vagus nerve when pressed against the skin of the neck.
Silberstein says doctors are exploring the use of vagus nerve
stimulation for a wide range of diseases and disorders, including
afflictions of the mind.
“More
and more, we’re learning how critical vagal activity is to attention
and mood,” says Field. Already, there’s evidence that stimulating the
vagus nerve may improve working memory or help people with attention deficit hyperactivity disorder. And since the early 2000s, the FDA has approved vagus nerve stimulation for the treatment of some forms of depression.
While
electronic stimulation holds promise — and, in some cases, is already
providing relief — for people with a range of ailments, Field says there
are plenty of ways to stimulate vagal activity without a device or
implant. “We know that massage and yoga promote parasympathetic nervous
system activity, which is vagal activity,” she says.
Her
research has shown that these and many related activities increase
vagal activity via pressure receptors buried beneath the surface of the
skin — receptors located throughout the body, and ones that only firm
pressure or a deep stretch can reach. She points out that light touching
or stroking is arousing, while a bear hug or powerful handshake are
inherently soothing. “A strong hug or a handshake promote
parasympathetic activity,” she says.
Silberstein
says that almost anything people find relaxing — meditation, deep
breathing — is also associated with heightened vagal activity and
parasympathetic nervous system activity. “We did studies in the past
showing that patients with migraine have impaired vagal activity,” he
says. “We tried to fix that by doing yoga or deep-breathing meditation,
and we found a lot of those things enabled us to activate the vagal
nerve.” On the other hand, stress and anxiety are associated with
depressed vagal activity, which may help to explain why these conditions
are linked with an increased risk for other maladies.
There’s
still a lot about the vagus nerve science doesn’t understand. But as
doctors uncover more of its secrets, these discoveries are revealing new
and more effective ways to relieve pain, inflammation, sadness, and
disease.
https://elemental.medium.com/science-confirms-that-the-vagus-nerve-is-key-to-well-being-c23fab90e211
https://elemental.medium.com/science-confirms-that-the-vagus-nerve-is-key-to-well-being-c23fab90e211
Elemental
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