Transcutaneous vagus nerve stimulation: The effect of different stimulus intensities on cardiac vagal activity

Transcutaneous Vagus Nerve Stimulation (tVNS) is a technology used to electrically and non-invasively modulate vagal activity. Given the importance of the vagus nerve in physiological, cognitive and in emotional regulatory processes, this stimulation method has recently been receiving increasing attention. However, studies
primarily addressing tVNS parameters have been scarce and the lack of knowledge about optimal stimulation parameters may represent an important limitation of this method. The present study focuses on different methods used so far in previous tVNS studies for setting the stimulation amplitude to be used in experiments and aims at identifying stimulation parameters for an optimal cardiac vagal activation. We were interested in the effect of tVNS on a physiological level using vagally mediated
heart rate variability (HRV) indicators, as well as in the subjective stimulation perception. Three experiments (within-subject designs, about 60 healthy participants each) have been carried out. In the first experiment, we investigated set stimulation intensities by comparing different amplitudes. In the second experiment, we
compared the set stimulation method with the free stimulation method, in which the participants were instructed to freely choose a comfortable intensity. The third experiment compared both methods with their respective sham stimulations. In the first experiment, a
main effect of time was found with an increase in HRV over time, but no significant difference between the conditions or interaction effect could be found. In the second experiment, a similar result could be observed by comparing both stimulation methods. Further results will
be presented as well as discussed.