A peer-reviewed thesis from the City University of New York tested whether transcutaneous auricular vagus nerve stimulation (taVNS) applied to the tragus produces measurable signs of parasympathetic activity compared with stimulation of the earlobe, a site chosen as an anatomically distinct control. Across several waveform conditions, only the 25 Hz waveform increased heart rate variability (HRV) during tragus stimulation relative to the earlobe condition. Heart rate and respiration showed no significant effects in any condition.
The finding gives partial support to the idea that vagal pathway activation depends on stimulation parameters. HRV responded selectively to one waveform; the absence of effects on heart rate and respiration limits how broadly the claim of parasympathetic engagement can be stated. The study does not establish that taVNS reliably engages the vagus across waveform conditions, and the mechanistic account linking cranial nerve afferents to brainstem nuclei such as the nucleus tractus solitarius and the locus coeruleus is theoretical framing, not something empirically tested here.
The design was a within-subject comparison, which controls for individual differences, but the abstract does not report sample size, blinding procedures, or full statistical details. Thesis-level peer review may also be less stringent than that applied to journal publications. The result should be treated as preliminary until replicated in a well-powered, pre-registered study. If the earlobe site is found to activate vagal afferents comparably to the tragus, or if the 25 Hz HRV effect does not replicate, the central finding would not stand.
The relevance to consciousness research rests on the anatomy: vagal afferents project to brainstem nuclei that feed neuromodulatory systems involved in arousal and attention. If taVNS can reliably shift autonomic state through those pathways, it would offer a peripheral handle on circuits considered relevant to conscious states. The present data do not demonstrate that, but they identify a specific parameter, 25 Hz at the tragus, and a specific measure, HRV, worth examining in larger studies.
Source: https://academicworks.cuny.edu/gc_etds/6819