The vagus nerve represents the main component of the parasympathetic nervous system, which oversees bodily functions. It establishes one of the connections between the brain and the gastrointestinal tract and sends information about the state of the inner organs to the brain via afferent fibers. It is the tenth cranial nerve, extending from its origin in the brainstem through the neck and the thorax down to the abdomen. Due to its long path through the human body, it has also been described as the “wanderer nerve”.
The vagus nerve has several different functions.
The four key functions of the vagus nerve are:
- Sensory: From the throat, heart, lungs, and abdomen.
- Special sensory: Provides taste sensation behind the tongue.
- Motor: Provides movement functions for the muscles in the neck responsible for swallowing and speech.
- Parasympathetic: Responsible for the digestive tract, respiration, and heart rate functioning.
Vagus nerve functions can be broken down into seven categories.
One of these categories is balancing the nervous system.
The nervous system can be divided into two areas: sympathetic and parasympathetic. The sympathetic side increases alertness, energy, blood pressure, heart rate, and breathing rate. The parasympathetic side, which the vagus nerve is heavily involved in, decreases alertness, blood pressure, and heart rate, and helps with calmness, relaxation, and digestion. As a result, the vagus nerve also helps with defecation, urination, and sexual arousal.
Other vagus nerve effects include:
- Communication between the brain and the gut: The vagus nerve delivers information from the gut to the brain.
- Relaxation with deep breathing: The vagus nerve communicates with the diaphragm. With deep breaths, a person feels more relaxed.
- Decreasing inflammation: The vagus nerve sends an anti-inflammatory signal to other parts of the body.
- Lowering the heart rate and blood pressure: If the vagus nerve is overactive, it can lead to the heart being unable to pump enough blood around the body. In some cases, excessive vagus nerve activity can cause loss of consciousness and organ damage.
- Fear management: The vagus nerve sends information from the gut to the brain, which is linked to dealing with stress, anxiety and fear. These signals help a person to recover from stressful and anxious situations.
There is preliminary evidence that vagus nerve stimulation is a promising treatment for refractory depression, post traumatic stress disorder, and inflammatory bowel disease. Treatments that target the vagus nerve increase the vagal tone and inhibit cytokine production. The stimulation of vagal afferent fibers in the gut influences monoaminergic brain systems in the brain stem that play crucial roles in major psychiatric conditions, such as mood and anxiety disorders.
Furthermore, there is preliminary evidence for gut bacteria to have beneficial effect on mood and anxiety, partly by affecting the activity of the vagus nerve. Since, the vagal tone is correlated with capacity to regulate stress responses and can be influenced by breathing, its increase through meditation and other modalities likely contribute to resilience and the decrease in mood and anxiety symptoms.
An increasing number of studies have shown benefits with relaxation-related treatment of Irritable Bowel Disease (IBD). For example, a randomized controlled trial of a relaxation-training intervention compared to a control group has shown decrease in pain as well as decreased anxiety levels and improvements in quality of life (206). Also, mindfulness-based therapy (207), a comprehensive mind-body program (208), meditation (209), mind-body alternative approaches (210), yoga (211), and relaxation response-based mind-body interventions (212) have shown to be beneficial for IBD patients. In addition, hypnotherapy, which increases vagal tone (213), has been effective in the treatment of IBD (12).
Read in depth:
Front. Psychiatry, 13 March 2018 | https://doi.org/10.3389/fpsyt.2018.00044
Vagus Nerve as Modulator of the Brain–Gut Axis in Psychiatric and Inflammatory Disorders
Sigrid Breit1†, Aleksandra Kupferberg1†, Gerhard Rogler2 and Gregor Hasler1*
- 1Division of Molecular Psychiatry, Translational Research Center, University Hospital of Psychiatry, University of Bern, Bern, Switzerland
- 2Department of Gastroenterology and Hepatology, University Hospital Zurich, Zurich, Switzerland