Abstract
When facing decisions to approach reward or to avoid punishment, we often figuratively go with our gut. While the impact of metabolic state such as hunger on motivated behavior is well documented, the role of vagal feedback signals originating from the gut in adjusting go/no-go behavior is still largely elusive. Consequently, we investigated the effect of non-invasive transcutaneous vagus nerve stimulation (tVNS) on approach and avoidance behavior using an established go/no-go reinforcement learning paradigm (Guitart-Masip et al., 2012). As part of an ongoing study, 28 healthy participants completed the task after receiving either tVNS or sham stimulation (randomized cross-over design). To estimate the effects of tVNS on go/no-go learning, we conducted a hierarchical logistic regression analysis and fitted a computational model. The logistic regression analysis showed that tVNS selectively reduced punishment learning, χ(1) =5.21, p =.021, regardless of the required action. Similarly, the computational model revealed a slightly reduced learning rate (LR) after tVNS (ΔLR =-0.09, p =.089). Nevertheless, a positive correlation between the action bias and the effect of tVNS on go responses (r =.475, p =.011) suggests that tVNS may strengthen a preponderant response bias. Moreover, tVNS had no effect on response time indicating that impaired punishment learning was not driven by changes in deliberation time. To conclude, our results highlight a novel role of vagal afferent input in modulating reinforcement learning. While impaired learning from punishments appears to be detrimental, it might contribute to the reported anti-depressive effects of tVNS by re-balancing action learning towards rewards.
