The only place on the body where the vagus nerve (VN) sends its only peripheral branch is on the outer ear. The auricle is where this VN branch surfaces to form a cutaneous receptive field in the pinna of the ear — an area responsive to peripheral nerve stimulation. Thus, the auricle allows for easy access for auricular (and transcutaneous auricular) vagus nerve stimulation (aVNS/taVNS), that relays the stimuli to the brainstem and higher brain regions via extensive projections to second and third order neurons within the brain (Mercante et al., 2018b). The ear may offer means for the most affordable non-invasive neuromodulation of the central nervous system via the auricular branch of the vagus nerve.
Owing to the importance of the vagus nerve, aVNS has broad potential for therapeutic neuromodulation:
Modulation of Nociceptive Processing | The inhibitory and desynchronizing actions of VNS, as well as enhanced brain plasticity, activated serotonergic pathways, and anti-inflammatory effects of VNS, can be hypothesized to counteract the maladaptive plasticity and inflammation of the central sensitization and thus to counteract pain hypersensitivity.
Modulation of Inflammation | Inflammation processes governed in part through neural reflex pathways (Tracey, 2009; Miller and Raison, 2015) with chronic inflammation and imbalance between pro-inflammatory and anti-inflammatory cytokines seems to be decisive in disease progression implicated in chronic diseases such as diabetes mellitus, and a major hindering factor in effective neuroprotection of the brain after stroke.
Modulation of Autonomic Function | Regulation of the parasympathetic over the sympathetic system has been identified as one of the therapeutic mechanisms of aVNS (Clancy et al., 2014; Kampusch et al., 2015a).
Modulation of Metabolic Syndrome | Reduced VN activity is hypothesized to underlie metabolic syndrome (De Couck et al., 2011), and aVNS is expected to reduce metabolic syndrome risks, such as obesity, elevated glucose levels, diabetes, elevated blood pressure, and increased inflammation
Modulation of Cardiovascular Effects | Specific aVNS effects of parasympathetic modulation on hemodynamic and cardiovascular control (Ness et al., 2000; De Ferrari and Schwartz, 2011).
Modulation of Cardioprotective Effects | Severity of myocardial reperfusion injury (implicated in ischemic myocardial infarction) is tightly related to parasympathetic hypoactivity and sympathetic hyperactivity (Florea and Cohn, 2014). Therefore, aVNS may be a potential therapeutic strategy (Byku and Mann, 2016).
Modulation of Psychometric Functions | In clinical trials, aVNS was shown to improve different psychometric functions, including well-being, alertness, cognitive performance while decreasing negative mood (Kothe, 2009); improved well-being, activity, and sleep in patients with chronic cervical pain (Sator-Katzenschlager et al., 2003) and with low back pain (Sator-Katzenschlager et al., 2004); reduction of anxiety in chronic pelvic pain patients (Napadow et al., 2012); improved personal/constitutional condition after abdominal and accident surgery (Szeles et al., 2001); positive affects on sleep (Becker, 2007); potential attenuation of postoperative cognitive dysfunction in elderly patients (Xiong et al., 2009).
Read the full paper on PubMed
Kaniusas E, Kampusch S, Tittgemeyer M, Panetsos F, Gines RF, Papa M, Kiss A, Podesser B, Cassara AM, Tanghe E, Samoudi AM, Tarnaud T, Joseph W, Marozas V, Lukosevicius A, Ištuk N, Šarolić A, Lechner S, Klonowski W, Varoneckas G, Széles JC. Current Directions in the Auricular Vagus Nerve Stimulation I - A Physiological Perspective. Front Neurosci. 2019 Aug 9;13:854. doi: 10.3389/fnins.2019.00854. PMID: 31447643; PMCID: PMC6697069.
Mercante B., Ginatempo F., Manca A., Melis F., Enrico P., Deriu F. (2018b). Anatomo-physiologic basis for auricular stimulation. Med. Acupunct. 30 141–150. 10.1089/acu.2017.1254
Tracey K. J. (2009). Reflex control of immunity. Nat. Rev. Immunol. 9 418–428. 10.1038/nri2566
Miller A. H., Raison C. L. (2015). The role of inflammation in depression: from evolutionary imperative to modern treatment target. Nat. Rev. Immunol. 16 22–34. 10.1038/nri.2015.5
Clancy J. A., Mary D. A., Witte K. K., Greenwood J. P., Deuchars S. A., Deuchars J. (2014). Non-invasive vagus nerve stimulation in healthy humans reduces sympathetic nerve activity. Brain Stimul. 7 871–877. 10.1016/j.brs.2014.07.031
Kampusch S., Kaniusas E., Szeles J. C. (2015a). Modulation of muscle tone and sympathovagal balance in cervical dystonia using percutaneous stimulation of the auricular vagus nerve. Artif. Organs 39 E202–E212. 10.1111/aor.12621
De Couck M., Mravec B., Gidron Y. (2011). You may need the vagus nerve to understand pathophysiology and to treat diseases. Clin. Sci. 122 323–328. 10.1042/CS20110299
Ness T. J., Fillingim R. B., Randich A., Backensto E. M., Faught E. (2000). Low intensity vagal nerve stimulation lowers human thermal pain thresholds. Pain 86 81–85. 10.1016/s0304-3959(00)00237-2
De Ferrari G. M., Schwartz P. J. (2011). Vagus nerve stimulation: from pre-clinical to clinical application: challenges and future directions. Heart Fail. Rev. 16 195–203. 10.1007/s10741-010-9216-0
Florea V. G., Cohn J. N. (2014). The autonomic nervous system and heart failure. Circ. Res. 114 1815–1826. 10.1161/CIRCRESAHA.114.302589
Byku M., Mann D. L. (2016). Neuromodulation of the failing heart: lost in translation? JACC Basic Transl. Sci. 1 95–106. 10.1016/j.jacbts.2016.03.004
Kothe A. R. (2009). Transcutaneous Vagus Nerve Stimulation - Change of Psychometric Parameters as a Function of Different Stimulation Regions. Doctoral thesis, Friedrich-Alexander-University, Stuttgart.
Sator-Katzenschlager S. M., Szeles J. C., Scharbert G., Michalek-Sauberer A., Kober A., Heinze G., et al. (2003). Electrical stimulation of auricular acupuncture points is more effective than conventional manual auricular acupuncture in chronic cervical pain: a pilot study. Anesth. Analg. 97 1469–1473. 10.1213/01.ane.0000082246.67897.0b
Sator-Katzenschlager S. M., Scharbert G., Kozek-Langenecker S. A., Szeles J. C., Finster G., Schiesser A. W., et al. (2004). The short- and long-term benefit in chronic low back pain through adjuvant electrical versus manual auricular acupuncture. Anesth. Analg. 98 1359–1364. 10.1213/01.ane.0000107941.16173.f7
Napadow V., Edwards R. R., Cahalan C. M., Mensing G., Greenbaum S., Valovska A., et al. (2012). Evoked pain analgesia in chronic pelvic pain patients using respiratory-gated auricular vagal afferent nerve stimulation. Pain Med. 13 777–789. 10.1111/j.1526-4637.2012.01385.x
Szeles J. C., Hoda M. R., Polterauer P. (2001). Application of electrostimulation acupuncture (P-Stim) in clinical practice.Pain News Austrian Pain Assoc. 1 1–3.
Becker M. (2007). Electroacupuncture and Autogenic Training for the therapy of Rheumatoid Arthritis: Randomised and Controlled Study. Doctoral dissertation, Medizinische Hochschule Hannover, Hanover.
Xiong J., Xue F. S., Liu J. H., Xu Y. C., Liao X., Zhang Y. M., et al. (2009). Transcutaneous vagus nerve stimulation may attenuate postoperative cognitive dysfunction in elderly patients. Med. Hypotheses 73 938–941. 10.1016/j.mehy.2009.06.033