Transcutaneous auricular vagus nerve stimulation for disorders of consciousness: a narrative review of neurophysiological mechanisms, clinical evidence, and future directions

Disorders of consciousness (DoC) following severe brain injury remain difficult to treat, and effective non-invasive therapeutic options are still limited. Transcutaneous auricular vagus nerve stimulation (taVNS) has recently emerged as a promising neuromodulation approach in this field. In this narrative review, we synthesize recent evidence on taVNS for DoC across four domains: neurophysiological mechanisms, multimodal monitoring evidence, clinical efficacy, and stimulation parameter optimization with safety considerations. Current mechanistic models suggest that taVNS may influence consciousness through the auricular branch of the vagus nerve, engaging brainstem nuclei such as the nucleus tractus solitarius and locus coeruleus, and subsequently modulating thalamo-cortical and large-scale cortical networks; this remains a biologically plausible working model rather than a validated causal pathway. Preliminary clinical data suggest that patients in a minimally conscious state may respond more often than those with unresponsive wakefulness syndrome/vegetative state; however, this is a subgroup-level signal-the only sham-controlled randomized trial to date found no significant overall between-group difference-and the evidence remains limited by small samples, protocol heterogeneity, and short follow-up. Multimodal tools including electroencephalography, functional near-infrared spectroscopy, heart rate variability, and serum biomarkers may improve mechanistic understanding and responder stratification, but integrated evidence within the same patient cohorts remains scarce. Overall, taVNS appears to be a promising adjunctive intervention for DoC, but its routine clinical application remains provisional until ongoing multicenter randomized trials clarify efficacy, durability, optimal stimulation parameters, and responder profiles.