Acute Transcutaneous Cervical but not Auricular Vagus Nerve Stimulation Increases Alpha Wave Brain Activity and Lowers Arterial Blood Pressure

Non-invasive vagus nerve stimulation (VNS) devices promise stress-relief through increased parasympathetic activity and a more relaxed mental state, associated with heightened alpha wave electroencephalogram (EEG) activity. The cervical vagus nerve (CVN) contains 5-6-times more Aβ-fibers than the auricular branch of the vagus nerve (ABVN). Additionally, the CVN contains afferent and efferent fibers while the ABVN is a purely afferent nerve. We hypothesized that hemodynamic, autonomic, and cerebral responses to cervical VNS are more pronounced than those to auricular VNS. Young healthy adults were randomized into a time control (n=10), a bilateral cervical VNS (n=9, 41 Hz, 100 μs, <40 mA), and two unilateral auricular VNS (10 Hz, 300 μs, 2-3 mA) groups with electrodes at the cymba conchae (n=7) or tragus (n=9) of the right ear. Systolic blood pressure (SBP) decreased only during cervical VNS (baseline: 134±15 mmHg vs. VNS: 120±16 mmHg, means±SD, n=9, P<0.05) which was associated with decreased low frequency (LF) SBP variability (baseline: 17.1±9.1 mmHg 2 vs. VNS: 7.8±9.1 mmHg 2 , means±SD, n=9, P<0.05). Cervical but not auricular VNS was followed by increased alpha wave activity (baseline: 6.2±1.8 μV vs. VNS: 7.7±1.7 μV, means±SD, n=9, P<0.05) recorded from the FP1 EEG electrode position. In conclusion, the hemodynamic, autonomic, and EEG responses to acute bilateral cervical VNS are more pronounced than those of unilateral auricular VNS, potentially, because the CVN contains 5-6-times more Aβ-fibers than the ABVN. Reduced SBP and LF SBP variability together with increased EEG alpha wave activity may indicate a more relaxed mental state during cervical VNS.