Autonomic Effects of Transcutaneous Auricular Vagus and Trigeminal Nerve Stimulation: A Randomized, Sham-Controlled, and Single-Blind Study

OBJECTIVE: This study aimed to investigate and compare the effectiveness of transcutaneous auricular vagus nerve stimulation (taVNS) and transcutaneous auricular trigeminal nerve stimulation (taTNS) in the autonomic nervous system in healthy individuals. MATERIALS AND METHODS: The study included 18 healthy participants (41 female, 39 male) aged between 20 and 50 years, without any acute or chronic illness. Participants were randomized to four groups as taVNS (n = 20), taTNS (n = 20), sham-taVNS (n = 20), and sham-taTNS (n = 20). taVNS and taTNS protocols were designed as follows: duration of bilateral auricular stimulation 30 minutes, current amplitude 250 microseconds, frequency 25 Hz, and current intensity 0.13 to 50 mA above threshold. The sham-taVNS and taTNS groups were designed so that the current intensity remained at 0 mA after the electrodes were placed and the device was switched on. Heart rate variability (HRV), pulse rate, and systolic (SBP) and diastolic blood pressure (DBP) were recorded at baseline and after interventions. RESULTS: Heart rate decreased in the taVNS and taTNS groups, and SBP decreased only in the taVNS group compared with baseline (p < 0.05). Root mean square of consecutive differences (RMSSD) increased significantly in taVNS and taTNS groups (p < 0.05). The post hoc analysis showed that taVNS was more effective at increasing RMSSD than was taTNS (p < 0.05). DBP was not changed in all groups (p < 0.05). No parameter changes were found in the sham groups (p < 0.05). CONCLUSIONS: This study showed that taVNS was more effective in decreasing SBP and increasing RMSSD than were taTNS and sham stimulation. More predictive insights into taVNS and taTNS will come from different stimulation areas and results from longer-term studies in future. CLINICAL TRIAL REGISTRATION: The clinical trial registration number of the study was NCT06730165.