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Vagus Nerve

Reviewed by Psychology Today Staff

The vagus nerve, the longest nerve in the body, originates in the brainstem and extends down into the abdomen. It monitors and receives information about the functioning of the heart, lungs, and other internal organs so that you can focus attention on other matters.

It is the duty of the vagus nerve to orchestrate bodily responses to keep you safe or warn you about danger before you even have a chance to think about it. Without your awareness, the brain scans the environment for cues of danger, pitching you into high alert to fight or flee or, in extreme situations, shutting you down. It also scans for cues of safety, which allow you enough calm to open you up to socially engage with others.

What Is the Vagus Nerve?

Vagus means wandering, and the vagus nerve, after it leaves the base of the brain, sends branches to the ears, the throat, the heart, the lungs, and the digestive tract, with stops along the way at the vocal cords and the diaphragm, before descending into the abdomen. The branches of the vagus nerve enable the organs to adjust instantly to the demands of a person’s internal and external environment.

The vagus nerve is why your heart races and stomach curdles when you sense a threat and why your breathing slows and your body relaxes when friends welcome you to their house. The vagus nerve is the key player in the autonomic nervous system controlling your internal organs.

The vagus nerve is a major pathway of the parasympathetic nervous system, which, along with the sympathetic nervous system, constitutes the autonomic nervous system. Normally, sympathetic and parasympathetic nerves act synergistically and together create the state of equilibrium known as homeostasis. Disruption of the balance of sympathetic and parasympathetic activity is characteristic of a number of physical disorders with a strong psychological component—irritable bowel syndrome, for example—and some therapies target stimulation of the vagus nerve as a way to restore physiologic, and psychologic, balance.

Containing both sensory and motor fibers, the vagus nerve is in charge of both sensations and movement. Through its many branches, it controls swallowing and speech. It carries the sense of taste and sensations felt by the ears. It is responsible for involuntary muscle and gland control of the viscera, encompassing the heart, the lungs, the esophagus, and the rest of the digestive tract. It controls breathing and heart function, including heart rate. It relays sensations originating in the cervix and other organs of the abdomen.

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Why Is the Vagus Nerve Important?

Because information flows both to and from the brain via vagal pathways, the vagus nerve can be thought of as a major mind-body highway. The many branches of the vagus nerve are increasingly seen as pathways for promoting or restoring health and ameliorating the physiologic unease that gives rise to anxiety and other negative mental states.

States of visceral calm get relayed up to the brainstem, which then transmits the information to more highly evolved brain structures, allowing full access to the brain’s means of expression and enabling social interaction—which has the effect of perpetuating the state of neural calm. But in potential danger states, such as completely novel environments, those higher systems turn off and we become defensive and on high alert: The vagal circuitry narrows our focus and prepares us to fight or flee—the so-called stress response.

If the danger is so overwhelming that there’s no escape or there’s a feeling of being trapped, a third circuit of vagal operations engineers a shutdown. In this out-of-focus, numb state, social contact becomes aversive. Such bodily responses are not voluntary, and often people are not aware of what triggered them, although they are likely aware that their heart is pounding or their body is trembling.

Because the vagus nerve operates bidirectionally, states of homeostasis and calm, which are necessary for restoration and growth, can be induced from the bottom up or the top down. That is, the brain can deploy cognitive and other strategies to dissipate states of bodily unease (top down), or it can activate the vagus nerve at a number of points in its path to create psychological comfort and a sense of safety (bottom up).

What Does the Vagus Nerve Do?

Defense is a major obligation of every living system, and humans are no different. It is the job of the autonomic nervous system to detect danger and keep us safe. Before we are even consciously aware of it, the autonomic nervous system detects threats and responds, enacting a defense strategy to help us survive. Activation of the stress response, setting off a cascade of physiologic changes to prepare the body for fast action if needed, is a hallmark of the strategy. So is an outpouring of signaling chemicals and pro-inflammatory compounds that circulate through the body, including the brain. Anxiety is the name we give to the visceral unease we feel under such conditions.

Many of the chemical changes stirred by the detection of threat act directly on the brain, jolting it into alertness, sharpening senses, prompting a search for something amiss—even setting off a sense of doom—and shutting down such higher brain functions such as decision-making and creativity. Heart rate, breathing, blood pressure, all go into high gear, readying the body for movement. The shifts in physiologic state in response to threat are kicked off by the sympathetic branch of the autonomic nervous system.

By contrast, the vagus nerve, the main component of the parasympathetic branch of the nervous system, is the architect of safety. It acts to down-regulates the response to threat, to restore visceral order and psychological calm. Its action is needed to enable renewal and growth. And in shutting down defenses, it sets the psychological stage for social interaction.

How does the vagus nerve influence mind-body interaction?

The vagus nerve connects the brain with the major organ systems of the body. It links mental and physical processes. It is the means by which the mind and body are physiologically inseparable; signals that affect one directly affect the other, although they find expression in different ways.

Among the many operations of the body and brain it controls, the vagus nerve is responsible for relaxing tension, counteracting activity of the sympathetic nerves and establishing the very positive state of homeostasis, sometimes called “rest and digest.” It down-regulates the response to stress, curbing the physiologic state of alarm and ushering in a state of calm experienced as a sense of safety, which the body needs for repair, growth, and reproduction.  The disturbed physiology that marks states of threat is often a player—sometimes an unrecognized one—in chronic physical and psychiatric disorders, giving the vagus nerve a huge role in maintaining health in the body and the brain.

What role does the vagus nerve play in the gut-brain axis?

The vagus nerve oversees digestion and is one of the main channels of connection between the brain and the gastrointestinal tract. Among many other actions, it ferries to the brain signals generated by the metabolic actions of the gut bacteria on specific types of food—one means by which diet plays an important role in mental health. The vagus nerve also conveys signals of other neuroactive substances secreted by the digestive tract; among the best known are those that control appetite. The vagus nerve also contributes to the immune defense of the gut.

The Mind-Body Highway

As a large neural pathway between much of the body and the brain, the vagus nerve operates automatically to control many functions. It is also susceptible to influence in multiple ways.

What role does the vagus nerve play in physical health?

Breathing. Heart rate. Blood pressure. Digestive functions including movement of food through the gut. All are controlled by the vagus nerve.

Vagal tone is a term often used to indicate the balance between sympathetic and parasympathetic (vagal) activity in relation to the heart, and it is assessed by measuring the heart’s ability to respond appropriately to situations that demand an increase or decrease in cardiac output and thus a faster or slower heart rate (heart rate variability). Good vagal tone allows the system to ramp up quickly as conditions demand (say, a sudden need to flee a dangerous situation) and to settle down after an experience of stress. Low vagal tone is a feature of inflammatory bowel disease, irritable bowel syndrome, and other disorders of the gastrointestinal tract.

What role does the vagus nerve play in mental health?

As the autobahn of mind-body interaction, the vagus nerve is a powerful modulator of mood, a major pathway of the stress response, and a participant in conditions as diverse as heart disease and vocal paralysis. The feeling of anxiety—the mental state of modern times— is a reflection of the agitated physiologic state created by threat and relayed to the brainstem via the autonomic nervous system. As it is interpreted by higher brain structures, the physiologic turmoil turns on a suite of negative emotions. Through the use of higher brain structures—memory, previous learning, networks of associations—people create narratives of worry to explain the visceral unease. Thoughts focus on problems and other bad things. People create catastrophic “what if…” scenarios having a whole range of negative outcomes. There may be a feeling of impending doom.

In the panoply of negativity turned on by the physiologic unease, people also develop negative feelings and beliefs about themselves. Researchers have documented that worriers display themes of personal inadequacy and low self-esteem. They believe that they lack control over events. And they lose confidence in their ability to solve problems. Responding to unease with worry sets off a downward spiral of distress from which it is often difficult to escape.

Mechanical activation of the vagus nerve, in which an implanted device delivers intermittent impulses to the vagus nerve, is currently used as a treatment of resistant depression. But there are many other ways to stimulate the vagus nerve noninvasively to restore mental health.

Stimulating the Vagus Nerve

Increasingly, scientists are coming to understand the connections between physiologic and psychologic states of distress, with their accompanying sense of threat, on the one hand, and states of physiologic and psychologic calm, with their accompanying sense of safety, on the other. As a result, the vagus nerve has come into sharp focus as providing effective, noninvasive ways of restoring physiologic and psychologic composure. As the commander-in-chief of the parasympathetic nervous system, the vagus nerve countervails systemic unease and the "fight-or-flight" stress responses to induce a state of calm and restore homeostasis.

It’s not just enough to remove the threat; the nervous system demands cues of safety. Through the application of specific maneuvers stimulating vagal pathways, the nervous system can be used to reset physiologic state. Shifting physiologic state restores access to all the higher cognitive capacities including memory and restores the capacity for social engagement.

What does stimulating the vagus nerve do?

Stimulation of the vagus nerve is medically well known as a means of regulating the excitability of nerve cells. It is currently used therapeutically to normalize heart rate in people subject to certain cardiac arrhythmias and to control refractory epileptic seizures. It is also sometimes used to treat resistant depression; imaging studies indicate it curbs overactivity of certain regions of the brain. Such treatment involves the use of a device—either implanted inside the chest cavity or noninvasively affixed to the skin— that delivers intermittent electrical impulses to the vagus nerve. There are, however, many simpler maneuvers (see How to stimulate the vagus nerve) that almost anyone can do to activate the vagus nerve and modulate vagal tone.

How does vagus nerve stimulation reduce stress?

When the body is in states of danger or even in complete shutdown, it is possible to restore calm and regain behavioral flexibility by redirecting vagal activity, which can be accomplished through a deceptively simple maneuver—breathing. Specifically, the effect requires breathing deeply and exhaling slowly, ideally so that the exhalation lasts twice as long as the inhalation.

By engaging the diaphragm, deep-breathing activates vagal pathways that counteract both the flight-or-fight stress response and behavioral shutdown. Most people respond to the experience or even the anticipation of stress in any form by stopping breathing and holding their breath. Breath-holding itself activates the fight/flight/freeze response; it also increases the sensation of pain, stiffness, anxiety, or fear.

Deep breathing allows people to feel “centered.” Such vagal breathing not only lowers defenses, relaxes the body, and slows heart rate but also gives people access to their higher mental powers; studies show that, among other things, it improves decision-making. The deep breathing can be done anytime, anywhere, to foster relaxation.

In diaphragmatic breathing, the belly expands and rises as the lungs fill with air. The movement of the diaphragm stimulates the calming circuit of the vagal nerve. Deep, slow breathing that moves the diaphragm is an integral part of many ancient meditation traditions. Yoga long ago incorporated the power of respiration—bellows breath is one exercise—to change physical and mental states. The ancients knew that it worked; they just didn’t know how it did.

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