Without getting under your skin: non-invasive stimulation activates the vagus nerve

Cervical non-invasive vagus nerve stimulation (nVNS) has emerged as a practical neuromodulation approach with FDA-cleared indications in primary headache disorders, yet skepticism persists over whether transcutaneous stimulation can reliably engage vagal fibers or whether observed benefits reflect nonspecific cervical activation. Here, we synthesize converging anatomical, biophysical, physiological, and clinical evidence demonstrating that nVNS does, in fact, activate vagal pathways without surgical implantation. We first review cervical vagus anatomy and the biophysical basis for target engagement, including ultrasound-measured nerve depth and multi-scale computational models showing that clinically relevant stimulation can recruit predominantly large myelinated vagal fibers. We then integrate mechanistic evidence across complementary modalities: functional imaging consistently modulates canonical vagal projection sites (including brainstem nuclei), electrophysiology demonstrates peripheral vagal recruitment and centrally transmitted evoked responses, immune studies reveal reproducible suppression of pro-inflammatory cytokines consistent with cholinergic anti-inflammatory reflex engagement, and autonomic biomarkers show shifts toward increased parasympathetic tone. Finally, we contextualize these mechanistic findings with sham-controlled randomized trials in cluster headache and migraine, where nVNS repeatedly outperforms sham for acute and preventive outcomes with a favorable safety profile. Together, these independent lines of evidence form a coherent mechanistic fingerprint that is difficult to reconcile with placebo or superficial muscle stimulation accounts. We conclude that nVNS provides a credible, scalable means of accessing vagal neurophysiology and represents a clinically validated, paradigm-shifting advance in bioelectronic medicine.