What is Vagus Nerve Stimulation?

In human body autonomic nervous system is related with important vital functions and it is controlled basicly by the hypothalamus, a smaller part of our brain. Autonomic nervous system is divided into two parts, which are called as sympathetic and parasympathetic, and they control the diameter of pupils, heart rate, contraction of the heart, diameter of vessels and airways, secretions and sweating, digestion, voiding, defecation, metabolism, reproduction etc. If stable functional dysfunction occurs in the system; hypertension, obesity, depression, chronic pain, sleep disorders, chronic fatigue, gastrointestinal disorders, immune system related disorders can be seen. The treatment of the functional impairment cures the diseases stated above in addition to epilepsy, addiction problems like disorders.

Nowadays stress (physical and psychososcial loading of the body) is seen as the primary factor causing functional disturbance in autonomic nervous system and frequently activates sympathetic nervous system in the body to make ‘’fight or flight’’ response.  In acute stress this is a life saving condition, but when the condition becomes chronic it results in psychososcial and physical disorders.

Transcutaneous vagus nerve stimulation activates noninvasively auricular afferent part of the 10th cranial nerve, vagus and the latter is the most important division of the parasympathetic system. Auricular vagus innervates medial part of tragus, concha and external ear canal, so electrical stimulation of the ear vagus can regulate overactivated sympathetic nervous system and by this way treat stress related disorders. When we consider the time, place variability and long duration of the stress sources, chronic stimulation of the vagus nerve can be expected to develop as a good method for protecting and improving the personal and communal health.

General Information

In our bodies, there is a system called as autonomic nervous system which works involuntarily (autonomous), adapts body to internal and external changes, controls vital structures like heart, lungs, vessels, bowels, reproductive organs. It is composed of two parts: one is the sympathetic nervous system which give rise to ‘’fight or flight’’ response especially in danger, attacking conditions in the external environment; and the other is the parasympathetic nervous system which calms the body, provides growing and developping, mostly has the internal properties, and is mentioned as ‘’rest and digest’’ shortly. The center of the autonomic nervous system is hypothalamus in the brain, a part of the limbic system. Hypothalamus controls lots of vital functions together with autonomic nervous system (Özden AV, 2015).

The nerves emanated from hypothalamus travel certain paths in brain and spinal cord, then stimulate the sympathetic and parasympathetic nerves which are dispersed to all body. Parasympathetic nervous system is composed of cranial nerves 3, 7, 9 and 10 with sacral nerves 2-4. Sympathetic nerves exit from the levels of spinal cord between thoracic 1 and lumbar 2. Sympathetic nervous system uses adrenalin and noradrenalin molecules in end-organs; parasympathetic nervous system uses acetylcholine instead. The functions of the two systems are summarized in the below table (Özden AV, 2015).

 

 

Functions of the sympathetic and parasympathetic nervous system
Sympathetic system Parasympathetic system
Pupil size Enlarges Constricts
Heart rate Elevates Decreases
Heart contraction Elevates Decreases
Vessels Enlarges or constricts Enlarges
Airways Enlarges Constricts
Secretions-sweating Elevates sweating Elevates secretions
Bowel movements Decreases Elevates
Voiding Blocks Causes
Defecation Blocks Causes
Lipid tissue Decreases Elevates
Blood glucose and fatty acids Elevates Generally decreases
Genital tract (woman) Orgasm Clitoral erection- Elevates secretions
Genital tract (man) Ejeculation-orgasm Erection

 

Vagus nerve has a great role in regulation of homeostasis. By the neuro-endocrine-immune connections it can control cardiorespiratory system, digestive system, inflammation, psychologic conditions and pain (Yuan ve diğ, 2015). Vagus nerve stimulation started in 19th century but the real usage was seen in 1990s for treatment of drug resistant epilepsy and depression.  In 2005 The US Food and Drug administration (FDA) approved left implanted vagus nerve stimulation for treatment resistant epilepsy and chronic resistant depression. In 2015 again, FDA accepted vagus nerve stimulation for obesity treatment. Vagus nerve stimulation is also suggested for heart insufficiency. Transauricular vagus nerve stimulation is approved in Europe for epilepsy and depression in 2010, for pain in 2012. Vagus nerve stimulation is being investigated for diseases like bipolar disorder, Alzheimer disease, insulin resistance, asthma, fibromyalgia, traumatic brain injury, stroke, tremor and kinetic disorders (Yuan ve diğ, 2015).

In their study in 2014, Clancy and her friends stimulated tragus with TENS current and found decreament of sympathetic activity. Busch et al (2013) showed that pain perception decreases when concha and tragus are stimulated. Straube et al (2015) saw that left concha stimulation 4 hours per day for 3 months decreases headache days more than 50%. Jacobs et al (2015) declares that transcutaneous vagus nerve stimulation improves memory in elderly. When we look at interrelation between depression, inflammation, metabolic syndrome and heart diseases, vagus nerve states in an important position (Howland RH, 2014).

As a result, in autonomic nervous system dysfunction condition; hypertension, obesity, chronic pain, depression, sleep disorders, chronic fatigue, gastrointestinal disorders, immune system related disorder can be seen. The treatment of the functional impairment cures the diseases stated above in addition to epilepsy, addiction problems like disorders. Stimulation of the afferent branch of the vagus nerve in the ear seems to have an important role in treatment of autonomic nervous system dysfunction. In the near future it is possible to see this method spreading to all over the World and constitute a huge portion in the present treatment options.

 

 

 

Sources

Busch V, Zeman F, Heckel A, Menne F, Ellrich J, Eichhammer P. The effect of transcutaneous vagus nerve stimulation on pain perception–an experimental study. Brain Stimul. 2013 Mar;6(2):202-9.

Clancy JA, Mary DA, Witte KK, Greenwood JP, Deuchars SA, Deuchars J. Non-invasive Vagus Nerve Stimulation in Healthy Humans Reduces Sympathetic Nerve Activity. Brain Stimulation 7 (2014) 871-877.

Howland RH. Vagus Nerve Stimulation. Curr Behav Neurosci Rep. 2014 June ; 1(2): 64–73.

Jacobs HIL, Riphagen JM, Razat CM, Wiese S, Sack AT. Transcutaneous vagus nerve stimulation boosts associative memory in older individuals. Neurobiology of Aging 36 (2015) 1860-1867.

Özden AV. Bazen Her Şey Sinirsel, Bedenimizi kontrol eden otonom sinir sistemine bir bakış. 2015, Agate Yayınları.

Straube A, Ellrich J, Eren O, Blum B, Ruscheweyh R. Treatment of chronic migraine with transcutaneous stimulation of the auricular branch of the vagal nerve (auricular t-VNS): a randomized, monocentric clinical trial. The Journal of Headache and Pain (2015) 16:63.

Yuan H, Silberstein SD. Vagus Nerve and Vagus Nerve Stimulation, a Comprehensive Review: Part II. (Headache 2015, doi: 10.1111/head.12650)

Yuan H, Silberstein SD. Vagus Nerve and Vagus Nerve Stimulation, a Comprehensive Review: Part I. (Headache 2015, doi: 10.1111/head.12647)

 

 

 

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