Vagus nerve stimulation increases vigor to work for rewards
Interoceptive feedback transmitted via the vagus nerve plays a vital role in motivation by tuning actions according to physiological needs. Whereas vagus nerve stimulation (VNS) reinforces actions and enhances dopamine transmission in animals, motivational effects elicited by VNS in humans are still largely elusive. Here, we applied non-invasive transcutaneous auricular VNS (taVNS) on the left or the right ear using a randomized cross-over design (vs. sham). During stimulation, 81 healthy participants had to exert effort to earn food or monetary rewards. We reasoned that taVNS enhances motivation and tested whether it does so by increasing prospective benefits (i.e., vigor) or reducing costs of action (i.e., maintenance) compared to sham stimulation. In line with preclinical studies, taVNS generally enhanced invigoration of effort (p = .004, Bayes factor, BF10 = 7.34), whereas stimulation on the left side primarily facilitated vigor for food rewards (left taVNS: Stimulation x Reward Type, p =.003, BF10 = 11.80). In contrast, taVNS did not affect effort maintenance (ps [≥] .09, BF10 < 0.52). Critically, during taVNS, vigor declined less steeply with decreases in wanting ({Delta}b = -.046, p = .031) indicating a boost in the drive to work for rewards. Collectively, our results suggest that taVNS enhances reward-seeking by boosting vigor, not effort maintenance and that the side of the stimulation affects generalization beyond food reward. We conclude that taVNS may enhance the pursuit of prospective rewards which may pave new avenues for treatment of motivational deficiencies.