Effects of Transcutaneous Vagus Nerve Stimulation, Neurofeedback, and their Combination on Cortisol, Anxiety, and Depression Subtypes in Non-Clinical Adults

Non-invasive neuromodulation techniques such as neurofeedback (NF) and transcutaneous vagus nerve stimulation (tVNS) are attracting growing interest for their potential to influence brain activity and emotional regulation. This pilot study investigated the individual and combined effects of these methods on psychological measures, electrophysiological markers, and salivary cortisol. Twenty healthy young adults (19 females, 1 male, aged 18–24) participated, with outcomes including psychological measures (anxiety and depression), EEG Alpha / Theta ratio, and salivary cortisol. NF was associated with significant reductions in anxiety and depressive symptoms. Notably, despite the NF protocol directly targeting Alpha / Theta oscillations, a significant increase in the Alpha / Theta ratio was observed only in the tVNS group, indicating a distinct bottom-up influence on neural dynamics. The combined intervention did not yield additional benefits, and cortisol levels remained unchanged. These preliminary findings suggest that NF and tVNS may operate through distinct pathways—NF influencing psychological outcomes via top-down regulation and tVNS modulating electrophysiological activity via bottom-up pathways. The absence of sham control conditions limits causal attribution of effects. Given the small sample size (n = 5 per group) and exploratory nature of this study, these results should be interpreted as hypothesis-generating and require replication in larger, adequately powered trials.