Non-invasive Access to the Vagus Nerve Central Projections via Electrical Stimulation of the External Ear: fMRI Evidence in Humans.
Level 3 - non-randomized controlled study
Non-randomized within-subject controlled experimental study in humans
PubMed 25573069 · doi:10.1016/j.brs.2014.11.018
What was done
Twelve healthy adults underwent two fMRI scans during a single session to compare brain activation between electrical stimulation sites (0.25 ms pulses, 25 Hz). Scan #1 tested the earlobe as an active control site, and scan #2 tested the left cymba conchae, an area innervated by the auricular branch of the vagus nerve. Region-of-interest analyses evaluated central vagal projections (corrected P < 0.01 for brainstem, P < 0.05 for forebrain), followed by a corrected whole-brain analysis (P < 0.05).
What was found
The abstract reports statistical thresholds but no quantitative effect sizes, percent signal changes, or coordinates. Compared to earlobe stimulation, cymba conchae stimulation resulted in significant activation of the ipsilateral nucleus tractus solitarii, bilateral spinal trigeminal nucleus, dorsal raphe, locus coeruleus, contralateral parabrachial area, amygdala, nucleus accumbens, and bilateral paracentral lobule. Bilateral deactivations were observed in the hippocampus and hypothalamus.
Why it matters
This study provides human neuroimaging evidence that non-invasive electrical stimulation of the cymba conchae accesses central vagal pathways that match classical projections previously identified in animal models.
Limits
The sample size is very small (n = 12) and limited to healthy volunteers. Stimulation order was fixed (earlobe scan #1, cymba conchae scan #2) rather than randomized or counterbalanced, creating risk of order effects or habituation. The abstract provides no numerical effect estimates or confidence intervals, and clinical outcomes were not evaluated.
Cited by
- supports Vagus nerve stimulation activates core brain arousal circuits, feeding directly or indirectly into structures such as the hypothalamus and locus coeruleus.