Secrets of the Vagus Nerve Revealed

This nerve is turning out to be
of central importance in health

 

New research invariably opens up new chapters in understanding the human body’s design and complexity.
As research reveals even greater levels of design and complexity in the human body,
evolution becomes even less tenable. This is very true of the vagus nerve.

 

by Jerry Bergman, PhD

The earliest evidence of vagus nerve function dates back 2,000 years ago when the ancient Roman physician Galen accidentally severed a set of nerves in a pig, stopping its squeals but not its squirming. We now know that Galen had severed the branch of the vagus nerve responsible for transmitting signals from the brain to the vocal cords, but not those causing wriggling and writhing. In the 2,000 years since, we have learned a great deal about this nerve. One thing is we realize that we have a lot more to learn about its many physiological functions.

What is the Vagus Nerve?

The vagus nerve is the longest and, by far, the most important cranial nerve in the body. The vagus nerve bundle of neural fibers begins at the brain stem and splits into two channels that run along either side of the neck. The two branches then rejoin at the heart before descending to the gut and most other organs. It is the main sensory superhighway that connects our brain to most of our vital organs (see Figure 1). It helps to regulate everything from the movement of food that passes through our intestines, to the steady beating of our heart. It controls certain reflex actions, including coughing, sneezing, swallowing, and vomiting. New research has revealed that it is even more complex than previously believed.

The goal of present research is to create a detailed map of the roughly 160,000 nerve fibers along its path. The researchers have concluded that achieving this goal “will revolutionize medicine.”[1]

Why the New Interest in a Nerve Discovered 2,000 Years Ago?

Recent research has revealed that the vagus nerve’s role is central to a far wider array of processes than previously realized. Besides monitoring organ function, it helps to discern facial expressions and even helps to regulate mood.

Most importantly, researchers are beginning to understand how it governs inflammation, the immune response that sometimes runs rampant in conditions including arthritis, heart disease, and Parkinson’s disease. It produces a connection between the brain and the gastrointestinal tract which is why emotions can cause an upset stomach. It also sends information about the state of our inner organs to the brain via afferent fibers (i. e., those nerves leading toward the central nervous system).

Vagus nerve stimulators use electricity to treat conditions ranging from epilepsy, depression, migraines, and obesity. Efforts to untangle its design are allowing researchers to map each of its branches, and even discover new specialized cell types they never knew existed. Not only do these insights help doctors to control inflammation, but they could open a whole new set of treatment programs.[2]

Success by Using Pulse Vagus-Nerve Stimulators                                                                  

In the late 1980s, it was demonstrated that implanting a vagus nerve stimulator reduces, or even eliminates, seizures from drug-resistant epilepsy. These stimulators use a pulse generator about the size of a poker chip which is implanted under the skin in the chest. The pulse generator sends electrical impulses by a wire to a cuff wrapped around the vagus nerve.[3] A similar implantable device for treatment-resistant depression has lessened symptoms for about 40 percent of patients who had previously tried four or more other treatments without success.[4]

Another example is the use of an implantable device to treat obesity: people using it lost about 8% more excess weight than those in the control group.[5] Most recently, the FDA approved a stimulator for regaining upper body movement after a stroke. Research also indicates that stimulators can be used to regulate blood pressure and even lower blood-sugar levels.

The vagus nerve’s ability to mediate inflammation is triggered when specialized neurons detect cytokines and, in response, send signals to the brain. These signals trigger the spleen to begin churning out white blood cells. This discovery indicates that electrode stimulators could interrupt the inflammation that causes rheumatoid arthritis.[6] One study found that 70% of patients had at least a 20% reduction in rheumatoid arthritis symptoms, and almost half saw a 50% improvement.[7]

The Design of the Vagus                                                                                                       

The vagus nerve contains both motor and sensory functions, and afferent neurons (those that carry information from sensory receptors of the skin and other organs toward the central nervous system (brain and spinal cord)). It also contains efferent neurons (those which carry motor information away from the central nervous system to the muscles and body glands). The nerve’s structure is complex, containing more than 160,000 fibers.

The right and left vagus nerves are the main neural components of the parasympathetic nervous system. They control involuntary body functions, including digestion, heart rate, and the immune system. The parasympathetic nervous system via the vagus nerves is the counterbalance to our stress response. It helps us calm down and relax and become more sociable. Their optimal functioning is essential for good physical and mental health.

Summary

The work applied to understanding the vagus nerve is another example of the steady progression of evidence for design, ingenious complexity, and the integration of all of the human body systems. The success of treatments stimulating the vagus nerve discussed above may be why acupuncture, yoga, tai chi, cold baths, and meditation all slow down respiration and cause the body to relax and calm down. In turn this slowdown affects certain signals traveling along the vagus nerve. These exercises may function by improving vagal tone, a measure of electrical activity along the vagus nerve which reveals vagus nerve activity.

The fact that electrical stimulation is able to improve a specific condition, or even a normal non-disease condition, indicates that some maladjustment in the body is causing health problems. In such cases the health problem is not due to the body design, but rather from an external factor, such as a dietary, emotional, or environmental stress.

The growth of knowledge from this research helps us to appreciate how the human body is well-designed, perhaps “over designed”.  The progress, as revealed by the few research programs discussed above, is one reason why the vagus nerve researchers are embarking on a three-year, 6.7-million dollar project funded by the U. S. National Institutes of Health (NIH) to map the vagus in its entirety. This includes identifying every single one of the 160,000 fibers and tracking their location along the vagus nerve’s meandering pathway.

Update 9/27/2023: The University of Auckland reports that the vagus nerve is active during exercise. This overturns previous assumptions that the complex nerve primarily governs ‘rest and digest’ functions of the parasympathetic nervous system. “The new research finds the parasympathetic and sympathetic nervous systems work together in exercise to help the heart pump harder and faster.” One of the study authors stated, “we can say that regular exercise can improve vagal activity and has beneficial effects.”

References

[1] Wade, Grace. 2023. Unraveling the secrets of the vagus nerve will revolutionize medicine. New Scientist, August 22. https://www.newscientist.com/article/mg25934530-500-unravelling-the-secrets-of-the-vagus-nerve-will-revolutionise-medicine/.

[2] Breit, Sigrid. 2018. Frontier Psychiatry, Volume 9. Section on Psychological Therapy and Psychosomatics, March 13.

[3] Pinrey, J., and J. Dean. 1990. Prevention of intractable partial seizures by intermittent vagal stimulation in humans: preliminary results. Epilepsia 31 (Suppl. 2):S40-43. doi: 10.1111/j.1528-1157.1990.tb05848.x.

[4] Reardon, J., et al. 2006. Vagus nerve stimulation (VNS) and treatment of depression: To the brainstem and beyond. Psychiatry 3(5):54-63.

[5] Badran, Bashar W.,, and Christopher W. Austelle. 2022. The future Is noninvasive: A brief review of the evolution and clinical utility of vagus nerve stimulation. Focus [an American Psychiatric Association (ASA) publication]20(1):3-7, January 25. Doi: 10.1176/appi.focus.20210023.

[6] Wade, Grace. 2023. Vagus nerve receptors may be key to controlling inflammation. NewScientist, January 18. https://www.newscientist.com/article/2355262-vagus-nerve-receptors-may-be-key-to-controlling-inflammation/.

[7] Koopman, Frieda A., et al. 2016. Vagus nerve stimulation inhibits cytokine production and attenuates disease severity in rheumatoid arthritis.. The Proceedings of the National Academy of Sciences 113(29):8284-8289, July 5.

---

Dr. Jerry Bergman has taught biology, genetics, chemistry, biochemistry, anthropology, geology, and microbiology for over 40 years at several colleges and universities including Bowling Green State University, Medical College of Ohio where he was a research associate in experimental pathology, and The University of Toledo. He is a graduate of the Medical College of Ohio, Wayne State University in Detroit, the University of Toledo, and Bowling Green State University. He has over 1,300 publications in 12 languages and 40 books and monographs. His books and textbooks that include chapters that he authored are in over 1,800 college libraries in 27 countries. So far over 80,000 copies of the 60 books and monographs that he has authored or co-authored are in print. For more articles by Dr Bergman, see his Author Profile.