Body of Research

Badran et. al. provide commentary on the growing interest in modulating the auricular branch of the vagus nerve (ABVN). Researchers clearly want to know which ear target is optimal for taVNS e tragus or cymba conchae. Although the authors note discrepancies — identified by Burger and Verkuil in the investigation of a manuscript by Peuker and Filler describing vagus innervation of the ear — that they have found difficult to resolve, their commentary offers insights.[1] 

First, recognizing the importance of the Peuker and Filler manuscript, it is also important to remember the body of work describing vagus preceding it — perhaps best exemplified with the Eastern medicine field of therapeutic auricular acupuncture. Ear acupuncture has been used for centuries and provides a body of supportive information (Wang 2012, Usichenko 2017, Asher 2010).[2-4] 

Second, the authors do not necessarily see the same conflict. That is to say, although the auricular branch of the vagus nerve (ABVN) may be unclear — either the tragus or the conchae — both locations likely engage some vagus fibers. Although cymba conchae targets may be 100% innervated by the ABVN (Peuker and Filler), ABVN fibers innervate the anterior wall of the external ear canal, landmarked by the tragus. 

Finally, our imaging study, and others (Badran 2018, Yakunina 2016), combined with heart rate data in adults (Badran 2018), indicate that tragus stimulation engages vagal afferents.[5-7]

The authors agree that we do not know the absolute best ear target for taVNS, as innervation of the ABVN remains unclear. More anatomical dissection studies would help provide more definitive resolution.  

The authors offer the following four basic fundamentals to consider in further investigations of transcutaneous auricular VNS targeting:[1]

1. anatomy
2. target engagement
3. parameter space
4. behavioral effects

Read the full commentary from Brain Stimulations at PMC

References:

[1] Badran BW, Brown JC, Dowdle LT, et al. Tragus or cymba conchae? Investigating the anatomical foundation of transcutaneous auricular vagus nerve stimulation (taVNS). Brain Stimul. 2018;11(4):947-948. doi:10.1016/j.brs.2018.06.003

[2] He W, Wang X, Shi H, Shang H, Li L, Jing X, et al. Auricular acupuncture and vagal regulation. Evid base Complement Alternat Med 2012;2012, 786839. [PMC free article] [PubMed] [Google Scholar]

[3] Usichenko T, Hacker H, Lotze M. Transcutaneous auricular vagal nerve stimulation (taVNS) might be a mechanism behind the analgesic effects of auricular acupuncture. Brain Stimul 2017;10(6):1042e4. [PubMed] [Google Scholar]

[4] Asher GN, Jonas DE, Coeytaux RR, Reilly AC, Loh YL, Motsinger-Reif AA, et al. Auriculotherapy for pain management: a systematic review and meta-analysis of randomized controlled trials. J Alternative Compl Med 2010;16(10): 1097e108. [PMC free article] [PubMed] [Google Scholar]

[5] Badran BW, Dowdle LT, Mithoefer OJ, LaBate NT, Coatsworth J, Brown JC, et al. Neurophysiologic effects of transcutaneous auricular vagus nerve stimulation (taVNS) via electrical stimulation of the tragus: a concurrent taVNS/fMRI study and review. Brain Stimul MayeJune 2018;11(3):492e500. [PMC free article] [PubMed] [Google Scholar]

[6] Yakunina N, Kim SS, Nam EC. Optimization of transcutaneous vagus nerve stimulation using functional MRI. Neuromodulation: technology at the neural interface. 2016. [PubMed] [Google Scholar]

[7] Badran BW, Mithoefer OJ, Summer CE, LaBate NT, Glusman CE, Badran AW, et al. Short trains of transcutaneous auricular vagus nerve stimulation (taVNS) have parameter-specific effects on heart rate. Brain Stimulation 2018. ISSN: 1935–861X. 10.1016/j.brs.2018.04.004 (in press). [PMC free article] [PubMed] [CrossRef] [Google Scholar]