Tragus or cymba concha? Debunking the anatomical myth
DOI: Pending DOI
Synopsis
Transcutaneous auricular vagus nerve stimulation (taVNS) demonstrated promising therapeutic effects in many conditions, yet the optimal stimulation site remains controversial. We systematically reviewed anatomical, biophysical, and clinical evidence comparing tragus and cymba concha stimulation. Findings indicated that auricular innervation is heterogeneous and functional vagal activation relies on stimulation parameters rather than anatomy alone. Tragus stimulation is similarly viable to the concha, with clinical studies consistently demonstrating meaningful effects. Our results suggest that the delivery of nerve stimulation, rather than anatomical location, is the primary determinant of efficacy.
Background
Transcutaneous auricular vagus nerve stimulation (taVNS) is an emerging neuromodulation technique targeting the auricular branch of the vagus nerve (ABVN) to modulate autonomic function. Early cadaveric anatomical mapping studies identified the cymba concha as a primary vagal innervation site, and led to its widespread adoption in taVNS protocols. However, these early findings are incomplete and do not present the comprehensive distribution of the ABVN. Subsequent neuroimaging studies further supported this mechanism by demonstrating brainstem activation following concha stimulation. The tragus, on the other hand, also showed promising autonomic effects through an increasing number of clinical studies.
Recent advances in anatomical and functional research challenge the notion of a single privileged stimulation site. Evidence suggests that auricular innervation is distributed and overlapping across regions. Neural activation may be influenced by stimulation parameters such as current density, electrode placement, and tolerability rather than anatomical fiber density alone10. These issues raised uncertainty regarding the relative importance of stimulation sites alone.
This review was conducted to systematically evaluate anatomical, biophysical, and clinical evidence to clarify how stimulation site selection in taVNS has evolved and to evaluate whether current data support preferential targeting of specific auricular regions.
Methods
A structured narrative review was conducted. Literature was systematically searched in Pubmed, Web of Science, and Scopus from inception to January 2026. Search terms included combinations of “transcutaneous vagus nerve stimulation”, “taVNS”, “auricular vagus nerve”, “tragus”, “cymba concha”, “auricular innervation”, and “vagus nerve anatomy”.
Studies were included if they reported anatomical, neuroimaging, biophysical, or clinical evidence relevant to auricular vagus nerve distribution or taVNS stimulation effects. Both experimental and clinical studies were considered. Review papers were included if they provided expert insights on anatomical or mechanistic explanations. Non-English articles were excluded.
After removal of duplicates, titles and abstracts were screened for relevance, followed by full-text assessment.
Results
240 studies were identified, of which 50 studies were included in the final analysis. Included papers were analysed for (1) anatomical distribution of the ABVN, (2) functional activation of the vagus nerve, (3) biophysical determinants of nervous activation, and (4) clinical outcomes from taVNS involving either tragus or cymba concha stimulation.
Several layers of evidence were evaluated. Firstly, current anatomical evidence indicated that auricular vagus nerve innervation is not confined to a single region but is distributed across multiple areas of the external ear, including the tragus, cymba concha, and the external auditory canal, in contrast to early cadaveric studies with an oversimplified presentation of the ABVN distribution. Studies also demonstrated substantial inter individual variabilities and overlapping innervation with other nerves (e.g. the greater auricular nerve), which could partly explain differences in taVNS outcomes.
Functional neuroimaging studies showed that both tragus and cymba concha stimulation could activate key vagal afferent pathways. These included the nucleus tractus solitarii and locus coeruleus. Both stimulation sites consistently demonstrated reliable engagement of central autonomic networks that were required for clinical effects.
Biophysical modelling studies indicated that neural activation during taVNS was primarily determined by current density, electrode configuration, and the properties of the underlying tissue rather than the fiber density alone. Studies had demonstrated that regions with lower presumed vagal density can still produce effective activation of the vagus nerve when the stimulation parameters were appropriately optimized13–15.
Clinical evidence further supported the importance of optimized stimulation parameters16. Studies across cardiovascular and autonomic indications showed both tragus and cymba concha have the potential to activate the vagus nerve provided signal deliveries are optimized. Clinical studies of tragus stimulation showed significant positive improvements in conditions like atrial fibrillation, anxiety, and postural orthostatic tachycardia syndrome. Overall, the findings of this review indicate that both tragus and cymba concha are viable stimulation sites. Clinical effectiveness is more closely associated with stimulation parameters and the delivery of the treatment.
Discussion
The findings of this review have important implications for both clinical application and future research of taVNS. We challenged the traditional view that the cymba concha represented a superior stimulation site based on anatomical considerations alone. Instead, current evidence supports a whole system-based approach where effective neuromodulation depends on the interactions between stimulation parameters, device/study design, and patient-specific factors.
The consistency in positive clinical outcomes observed in studies that employed tragus stimulation suggests that this stimulation site may offer practical advantages, such as accessibility, tolerability, and ease of achieving effective stimulation intensities and warrants adequate anatomical and neurotracing investigations for this region. In conclusion, both tragus and cymba concha are valid targets for taVNS. Current evidence strongly supports that effective stimulation delivery, rather than anatomical site alone, is the key determinant of obtaining positive therapeutic outcomes.
Disclosures
All authors were employees or consultants of Parasym Ltd at the time of this writing.
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