Transcutaneous auricular vagus nerve stimulation, tolerability, and the Alpha/Theta EEG ratio: a controlled pilot study relevant to emotion regulation

Background Anxiety and depression are both characterised by difficulties in emotion regulation, associated with altered cortical oscillatory activity. Transcutaneous auricular vagus nerve stimulation (taVNS) may modulate these dynamics, but few studies have examined stimulation intensity alongside both tolerability and EEG outcomes. Methods In this controlled pilot, ten healthy female adults (21.1 ± 1.8 years) were randomized to taVNS (n = 5) or a waitlist control (n = 5). The taVNS group completed eight 30-minute left tragus sessions over four weeks (20 Hz, 200 μs, 14–25 mA, individually titrated), with Alpha/Theta and Theta/Beta ratios derived from resting-state EEG at Cz. We applied False Discovery Rate (FDR) correction across the exploratory comparisons. Results Protocol completion was 100% across 40 sessions. Of 39 stimulation-related observations, 29 were tolerability or adverse-event symptoms, predominantly CTCAE Grade 1 (86.2%); 10 were self-reported sensations of pulse change, recorded separately. None was serious. Within-group change in the taVNS group was not significant (exact p = .063 for both ratios). Stimulation intensity did not show a positive dose-response. Between-group comparisons of change scores favoured taVNS for both ratios (both U = 25, exact p = .008; Hodges-Lehmann median difference 0.56, 95% CI [0.12, 0.90] for Alpha/Theta) and remained significant after FDR correction. Conclusion The protocol was completed by all five stimulated participants without serious adverse events under individual titration to tolerability (14–25 mA). We found preliminary effects on an EEG index relevant to emotion regulation, providing a quantitative basis for powering sham-controlled trials in clinical emotional dysregulation.