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Concurrent taVNS-fMRI Revealed Similar Brain Activation Patterns Elicited by Stimulation of the Mastoid and the Cymba
Xiaolong Peng1, Stewart S Cox1, Falon Sutton1
1Department of Psychiatry and Behavioral Sciences, Medical University of South Carolina, Charleston, SC, USA.
Background:
Transcutaneous auricular vagus nerve stimulation (taVNS) is a noninvasive neuromodulation technique that modulates central vagal and attentional circuits through stimulation of the auricular branch of the vagus nerve (ABVN). Although the cymba conchae is the most common target due to its dense ABVN innervation, its variable surface region and irregular shape complicate electrode placement and consistent current delivery. The mastoid process, located posterior to the auricle, offers easier accessibility and a larger stimulation surface, but the neural effects of its stimulation remain unclear.
Objective:
To determine whether mastoid stimulation elicits brain activation patterns comparable with traditional cymba stimulation.
Materials And Methods:
In this single-blinded, sham-controlled study, 24 healthy participants received stimulation at three sites (i.e., cymba conchae, mastoid process, and earlobe) in a block-design paradigm (30-second "ON"/"OFF" cycles), whereas functional MRI data were collected concurrently to assess whole-brain activation patterns and network-specific responses.
Results:
Both mastoid and cymba stimulation produced highly similar spatial patterns of brain activation, with activation in the anterior insula and temporoparietal junction, and deactivation in the sensorimotor cortex. Earlobe stimulation (sham condition) also elicited a similar spatial pattern of brain activation, but substantially weaker compared with mastoid and cymba stimulation. No adverse events were reported.
Conclusions:
Our findings show that mastoid stimulation elicits neural activation patterns comparable to cymba stimulation, engaging core vagal and attentional networks. These results suggest that the mastoid process may serve as a feasible and accessible alternative stimulation site for taVNS, potentially improving wearability, reproducibility, and patient treatment adherence in future clinical applications.
