Stimulation of the vagus nerve reduces learning in a go/no-go reinforcement learning task

Abstract

When facing decisions to approach rewards or to avoid punishments, we often figuratively go with our gut, and the impact of metabolic states such as hunger on motivation are well documented. However, whether and how vagal feedback signals from the gut influence instrumental actions is unknown. Here, we investigated the effect of non-invasive transcutaneous vagus nerve stimulation (tVNS) vs. sham (randomized cross-over design) on approach and avoidance behavior using an established go/nogo reinforcement learning paradigm (Guitart-Masip et al., 2012) in 39 healthy, participants after an overnight fast. First, mixed-effects logistic regression analysis of choice accuracy showed that tVNS acutely impaired decision-making, p = .045.Computational reinforcement learning models identified the cause of this as a reduction in the learning rate through tVNS (∆α = -0.092, pboot = .002), particularly after punishment (∆αPun = -0.081, pboot = .012 vs. ∆αRew = -0.031, p = .22). However, tVNS had no effect on go biases, Pavlovian response biases or response time. Hence, tVNS appeared to influence learning rather than action execution. These results highlight a novel role of vagal afferent input in modulating reinforcement learning by tuning the learning rate according to homeostatic needs..

Vagus nerve stimulation boosts the drive to work for rewards

“…Instead, taVNS increases the drive to work for rewards, particularly when they are wanted less, suggesting a boost in the utility of effort. These motivational effects are well in line with the hypothesized taVNS-induced increase in dopamine tone 13,30,31 , although this link needs to be directly investigated in future research. Our results shed light on the role of peripheral physiological signals in regulating instrumental behavior 3,4,16,36,37 and highlight the potential for non-invasive brain stimulation techniques to improve aberrant reward function.…”

“…Compared to implanted VNS, similar therapeutic effects have been reported after taVNS 27 – 29 . In line with the hypothesized potential of VNS to alter motivational processes, we recently found that taVNS affects value-based learning in a go/no-go reinforcement learning task 13 . Thus, non-invasive taVNS may provide an effective means to study the endogenous regulation of motivation according to homeostatic needs.…”

“…Next, participants completed a food-cue reactivity task (~20 min), before they performed the effort task (~40 min). Moreover, participants completed a reinforcement learning task 13 . Since the default stimulation protocol of the NEMOS taVNS device alternates between 30 s on and off phases, the off phases were manually shortened to correspond to the duration of the VAS ratings between effort phases during the task.…”

“…At the same time, acute VNS has reinforcing properties leading to sustained self-stimulation and conditioning preferences for flavors or places via a dopaminergic mechanism 3,11 . Furthermore, activation of vagal afferents regulates learning and memory in rats and humans suggesting a role in reward seeking 12,13 . Therefore, chronic reductions in food intake could be linked to acute increases in motivational drive by a combination of afferent and efferent effects.…”

Does non-invasive vagus nerve stimulation affect heart rate variability? A living and interactive Bayesian meta-analysis

“…For example, taVNS boosted mood after effort exertion, highlighting the vagus nerve's role in modulating interoceptive feedback signals (Ferstl et al, 2021). In addition, taVNS modulated reinforcement learning (Kühnel et al, 2020), facilitated invigoration to work for food and monetary rewards (Neuser et al, 2020) and enhanced delay discounting for individuals with low positive mood (Steenbergen et al, 2020). Although taVNS has been shown to evoke a variety of intended behavioral effects in healthy as well as in clinical samples, the physiological processes underlying the effects of taVNS are still largely elusive (Burger et al, 2020).…”