How can a small patch of skin on the ear serve as a site for vagus nerve stimulation? A branch of the vagus nerve reaches the ear and carries sensory information from it to the brainstem. Transcutaneous auricular vagus nerve stimulation (taVNS) uses electrodes on the ear to deliver electrical pulses intended to activate this auricular branch of the vagus nerve (ABVN).

Where the electrode sits determines which area of nerve supply lies beneath it. The cymba conchae is often a preferred site because its vagal nerve supply is relatively well documented, and stimulation there produces responses in related brainstem regions. Human studies comparing it with sites such as the tragus and ear canal have also found advantages worth considering.

To understand why the cymba conchae has become an important target in taVNS research, it is useful to first look at its location and the nerve supply beneath the skin.

Cymba Conchae: Definition and Location

In Figure 1, the arrow labeled “Cymba conchae” points to the small hollow above the crus of the helix, the ridge that crosses the concha. The larger hollow below it is the cavum conchae, labeled “Cavity of conchae.” The tragus is the small projection in front of the ear canal opening.

These landmarks are close together, but their nerve supply differs. They help us locate the electrode on the surface; to understand what lies beneath it, we need to look under the skin.

The cymba conchae is the upper part of the conchal bowl of the outer ear. Although the cymba conchae, cavum conchae, and tragus are close together, they represent different anatomical regions with different sensory nerve distributions.

Figure 1. The crus of the helix divides the concha into upper and lower parts. The cymba conchae lies above it, and the cavum conchae, labeled “Cavity of conchae,” lies below it. The tragus sits in front of the ear canal opening.

Why Does the Nerve Supply of the Cymba Conchae Matter?

The cymba conchae contains the auricular vagal branch that stimulation aims to reach.

Several nerves provide sensation to the outer ear. Alongside the auricular vagal branch are the great auricular nerve from the cervical plexus and the auriculotemporal nerve, a branch associated with the trigeminal nerve. Moving an electrode can therefore change the mix of nerves exposed to stimulation.

In 2002, Peuker and Filler dissected 14 ears from seven cadavers and traced the origins of the nerves supplying the outer ear. The researchers exposed the nerves, traced their origins, then colored and photographed them before compiling a map of the ear. The colored territories reflected nerves they had followed through the tissue.

In these specimens, the cymba conchae was supplied exclusively by the auricular vagal branch. The cavum conchae differed: 45% had an exclusively vagal supply, while 55% also received branches from the great auricular nerve. A single ridge separates the two hollows, yet their nerve supply was different.

Figure 2. Green marks the territory associated with the auricular vagal branch, and blue marks the auriculotemporal nerve territory. Much of the remaining area is supplied mainly by the great auricular nerve. The colored boundaries summarize classic anatomical descriptions and are approximate.

The boundaries on a nerve map do not confine electrical current to the same colored areas. Even where the sensory supply comes mainly from one nerve, electrode placement and current still affect which fibers are stimulated. Nor can observations from 14 ears tell us that everyone has exactly the same anatomy.

Finding the nerve in the cymba conchae raises a further question. What happens in the brainstem when electrical pulses are applied to the skin above it?

What Happens During Cymba Conchae Stimulation?

Stimulation at the cymba conchae can produce a response well beyond the ear. In a human study by Frangos and colleagues, stimulation of the left cymba conchae produced greater activity than earlobe stimulation in vagus-related regions, including the nucleus of the solitary tract and the locus coeruleus.

The nucleus of the solitary tract (NTS) lies in the brainstem, receives information carried by the vagus nerve, and has connections with the locus coeruleus (LC). The LC is involved in noradrenaline regulation and functions such as arousal and attention. Changes in these regions during ear stimulation can help reveal how stimulation affects related pathways in the brain.

In 2015, Frangos and colleagues studied 12 healthy adults who received stimulation at the left cymba conchae and the earlobe. The team recorded brain responses using functional magnetic resonance imaging (fMRI). The earlobe was a useful comparison because it produces a sensation when stimulated but lacks an auricular vagal supply in classic anatomical descriptions. Comparing the two sites helps distinguish the response to cymba conchae stimulation from the effects of feeling stimulation on the ear more generally.

fMRI measures nerve activity indirectly through changes in blood oxygenation. When an area “lights up” in an image, that reflects a corresponding change in the blood oxygen signal; it does not identify the individual nerve fibers activated in the ear. This study observed responses in the NTS, LC, and other regions, but did not measure whether symptoms of a particular disease improved.

The ear’s connections with the rest of the body sometimes show up in unexpected ways. Some people cough when their external ear canal is stimulated. This is Arnold’s ear-cough reflex, which involves sensory input through the auricular vagal branch. A stimulus in the ear can trigger a cough elsewhere in the body. During electrical stimulation of the cymba conchae, however, a person’s sensations cannot tell us exactly what is happening in the brain. Imaging allows researchers to observe those changes.

How Does the Cymba Conchae Compare With Other taVNS Stimulation Sites?

The cymba conchae is not the only ear location explored for transcutaneous auricular vagus nerve stimulation (taVNS). Both the tragus and ear canal have also attracted interest as stimulation sites because they contain different combinations of sensory nerve supply and may produce different responses.

In a study of 37 people, the cymba conchae was the only site that met the statistical significance threshold against the earlobe control in both the nucleus of the solitary tract (NTS) and the locus coeruleus (LC). The inner tragus met that threshold only in the NTS. The lower rear wall of the ear canal met it in neither region.

Published in 2017 by Yakunina and colleagues, the study tested four locations on the left ear in the same healthy participants: the inner tragus, the lower rear wall of the ear canal, the cymba conchae, and the earlobe. The team then examined the same brain regions for each location.

Having each person receive stimulation at different sites reduced the influence of differences between separate groups of people. This design allowed researchers to compare responses between locations within the same individuals.

Table 1. Comparisons of mean brainstem t-values between each stimulation site and the earlobe control within the same study. [4]

“Significant” in the table means that the statistical difference in brain-region activity between that site and the earlobe met the study’s threshold. The mean t-value does not tell us what percentage of nerves were activated. A result that is not statistically significant does not mean there was no response.

The tragus falling short of that threshold in the LC does not mean it produced no response there. Brain-imaging data vary. Observing a change and establishing a statistical difference from the earlobe are separate things.

Likewise, a significant difference between the cymba conchae and the earlobe does not automatically establish one between the cymba conchae and the tragus. Deciding which of those two sites performs better requires a direct comparison and a clear outcome of interest.

For the two brainstem regions examined in this experiment, the cymba conchae’s results make it a site worth considering.

The strongest practical case for the cymba conchae comes from studies that place it beside other ear targets and measure what changes. García de Gurtubay and colleagues did this in 26 healthy volunteers. They stimulated the cymba conchae alone, the cymba and cavum conchae together, and the earlobe, then recorded vagus somatosensory evoked potentials (VSEPs).

Clear responses appeared whenever the cymba conchae was included. Neither earlobe condition produced a measurable VSEP. Covering the neighboring cavum conchae increased the VSEP amplitude, and the larger electrode was more comfortable at higher current levels.

That finding matters for device design. A wider contact can recruit more fibers and spread charge over a larger surface. Yet the cymba conchae remains the anchor of the setup. It has the clearest vagal anatomical rationale, it generated a reproducible response on its own, and adding the cavum broadened coverage rather than replacing the cymba target.

VSEP amplitude measures an immediate electrical response in healthy volunteers, so it cannot predict clinical benefit by itself. Taken together with the anatomical and fMRI findings already discussed, however, these studies help explain why the cymba conchae remains one of the most commonly studied targets for taVNS.

Figure 4. Stimulation topographies and electrode sizes tested by García de Gurtubay et al. CC indicates simultaneous cymba and cavum conchae stimulation, C indicates cymba stimulation, and L indicates earlobe stimulation; X and S indicate extra-large and small electrodes.

What Does Current Evidence Support About Cymba Conchae Stimulation?

The cymba conchae is considered an important taVNS target because multiple lines of evidence support its use. Anatomical studies have identified a strong relationship between this region and the auricular vagal branch. Human imaging studies have observed responses in vagus-related brain regions, and physiological studies have measured responses when the cymba conchae is included in stimulation.

However, stimulation location is only one part of a taVNS protocol. Electrode placement, stimulation parameters, current intensity, and individual anatomy all influence the final response.

The structures beneath the cymba conchae help explain why the exact placement of an electrode matters. Nerves in the cymba conchae run between the epidermis and cartilage, with blood vessels nearby. Their paths and depths are difficult to show on a surface map of the ear. Three-dimensional imaging offers a view inside this small hollow.

In 2020, Dabiri and colleagues used high-resolution episcopic microscopy (HREM) to reconstruct a series of tissue sections as a three-dimensional model. Figure 3 comes from one cymba conchae specimen. The model shows the relationship between the epidermis, cartilage, nerves, and blood vessels beneath the stimulation site.

Figure 3. A three-dimensional reconstruction of cymba conchae tissue shows the spatial relationships between the epidermis, nerves, blood vessels, and cartilage. Colors distinguish the structures; the green nerves lie below the skin surface.

Following the green structures reveals nerves running below the epidermis, near blood vessels. The electrode rests on the ear’s surface, while the tissue it aims to influence has depth. Even within the cymba conchae, the precise contact point and the position of the second electrode remain relevant to the stimulation setup.

This image shows the internal structure of one specimen; the arrangement may differ between people. Green identifies nerves, but their appearance alone cannot establish whether each branch comes from the vagus nerve.

Once the cymba conchae has been selected, stimulation still has an intensity and a rhythm. In comparative studies, researchers adjusted current according to what each participant felt at each location because different parts of the same person’s ear may respond differently to the same stimulation level.

In one comparison study, electrodes delivered pulses at 25 Hz, or 25 pulses per second. Each pulse lasted 500 μs, equivalent to 0.5 milliseconds. Stimulation continued for 30 seconds, followed by a 60-second rest. Four cycles made up one six-minute scan.

The researchers first measured the level at which a participant could just feel the stimulus and the level at which it became painful. These were the sensory and pain thresholds. For the experiment, current was set 0.1 mA below the pain threshold, allowing the intensity at each site to reflect the participant’s tolerance.

With this approach, the average current was 0.91 mA at the cymba conchae and 0.77 mA at the tragus, a statistically significant difference. Brain responses were therefore recorded under conditions in which both location and actual current differed. The differences in response cannot all be attributed to location alone.

Stimulation also requires two electrodes. When researchers stimulated the tragus, ear canal, or cymba conchae, the second electrode sat on the outer tragus. For earlobe stimulation, it sat on the back of the earlobe. Both positions influence how current passes through tissue, so “cymba conchae stimulation” also involves a choice about where to place the second electrode.

Taken together, current evidence supports the cymba conchae as a well-studied and anatomically supported target for taVNS. At the same time, the effectiveness of stimulation depends on the complete setup, including electrode placement, stimulation parameters, and the outcome being measured.

Why Do taVNS Devices Target the Cymba Conchae Region?

The cymba conchae deserves attention in taVNS device design because this small hollow contains the auricular vagal branch that stimulation aims to reach, and human studies have observed responses in related brainstem regions when it is stimulated.

Auricular vagus nerve stimulation aims to use sensory nerves in the ear to send signals toward the brainstem. The exclusively vagal supply reported in the classic anatomical study made the cymba conchae a suitable candidate. Later human experiments found responses in regions including the nucleus of the solitary tract (NTS) and the locus coeruleus (LC) compared with earlobe stimulation. These regions are associated with incoming vagal signals, giving researchers a reason to keep this site in focus.

When tested alongside the tragus and ear canal in the same experiment, the cymba conchae was also the only site to meet the statistical significance threshold against the earlobe control in both the NTS and the LC. For approaches intended to influence these brainstem pathways through ear stimulation, it remains a site worth considering.

Its nerve supply and the responses observed in people help explain why the cymba conchae is so often chosen. However, site selection is only one part of a stimulation protocol. Electrode placement, contact area, stimulation intensity, and individual anatomy also affect the result.

Some taVNS devices extend stimulation coverage beyond the cymba conchae to include the neighboring cavum conchae. By bringing both regions into a single earpiece, this approach provides broader coverage of the concha while keeping the cymba conchae as a primary target.

Considering both the cymba conchae and surrounding conchal structures allows device designs to account for anatomical variation while maintaining focus on regions associated with vagal sensory pathways. The anatomy discussed throughout this article helps explain why the cymba conchae remains a central focus in taVNS research and device development.

References

[1] Peuker, E. T.; Filler, T. J. — The nerve supply of the human auricle — Clinical Anatomy, 15(1), 35–37 — 2002. https://doi.org/10.1002/ca.1089

[2] Butt, M. F.; Albusoda, A.; Farmer, A. D.; Aziz, Q. — The anatomical basis for transcutaneous auricular vagus nerve stimulation — Journal of Anatomy, 236(4), 588–611 — 2020. https://doi.org/10.1111/joa.13122

[3] Frangos, E.; Ellrich, J.; Komisaruk, B. R. — Non-invasive access to the vagus nerve central projections via electrical stimulation of the external ear: fMRI evidence in humans — Brain Stimulation, 8(3), 624–636 — 2015. https://doi.org/10.1016/j.brs.2014.11.018

[4] Yakunina, N.; Kim, S. S.; Nam, E.-C. — Optimization of Transcutaneous Vagus Nerve Stimulation Using Functional MRI — Neuromodulation, 20(3), 290–300 — 2017. https://doi.org/10.1111/ner.12541

[5] Mercante, B.; Deriu, F.; Rangon, C.-M. — Auricular Neuromodulation: The Emerging Concept beyond the Stimulation of Vagus and Trigeminal Nerves — Medicines, 5(1), 10 — 2018. https://doi.org/10.3390/medicines5010010

[6] Dabiri, B.; et al. — High-Resolution Episcopic Imaging for Visualization of Dermal Arteries and Nerves of the Auricular Cymba Conchae in Humans — Frontiers in Neuroanatomy, 14, 22 — 2020. https://doi.org/10.3389/fnana.2020.00022

[7] García de Gurtubay, I.; Bermejo, P.; Lopez, M.; Larraya, I.; Librero, J. — Evaluation of different vagus nerve stimulation anatomical targets in the ear by vagus evoked potential responses — Brain and Behavior, 11, e2343 — 2021. https://doi.org/10.1002/brb3.2343