Activating the body–brain axis: auricular vagus nerve stimulation facilitates learning from reward in health and depression

The decisions we make are shaped by our internal states. The vagus nerve, as the main neuronal connection between body and brain, is hypothesized to influence reward learning and decision-making based on signals from internal organs, providing a new target at the body-brain interface. This renders the vagus nerve a promising target to address reward dysfunction in mental health conditions such as major depressive disorder (MDD). In a randomized, sham-controlled within-subject design, we examined the effects of non-invasive transauricular vagus nerve stimulation (taVNS) on reward learning in a well-established probabilistic selection task in both healthy individuals (N=44) and individuals with major depressive disorder (N=53). We found that taVNS increased reward-guided choices across all participants. To unravel the underlying learning behavior, we fitted a reinforcement-learning drift-diffusion model (RLDDM) and estimated positive and negative learning rates. Positive learning rates at baseline were lower in MDD patients compared to healthy controls. taVNS selectively increased positive learning rates in MDD patients only. In line with rodent and previous human work, these findings indicate that stimulation of the vagus nerve influences reward-guided behavior in mental health conditions and provide crucial evidence for a new target to address impairments in reward learning.