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

Abstract

<jats:title>Abstract</jats:title><jats:p>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/no-go 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, <jats:italic>p</jats:italic> = .045. Computational reinforcement learning models identified the cause of this as a reduction in the learning rate through tVNS <jats:italic>(Δα</jats:italic> = −0.092, <jats:italic>p</jats:italic><jats:sub><jats:italic>boot</jats:italic></jats:sub>= .002), particularly after punishment <jats:italic>(Δα</jats:italic><jats:sub><jats:italic>Pun</jats:italic></jats:sub><jats:italic>=</jats:italic> −0.081, <jats:italic>p</jats:italic><jats:sub><jats:italic>boot</jats:italic></jats:sub>= .012 vs. <jats:italic>Δα</jats:italic><jats:sub><jats:italic>Rew</jats:italic></jats:sub><jats:italic>=</jats:italic> −0.031, <jats:italic>p</jats:italic> = .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.</jats:p>

Vagus nerve stimulation increases vigor to work for rewards

“…Moreover, similar therapeutic effects have been reported for taVNS compared to implanted cervical VNS (Fang et al, 2016;Liu et al, 2016;Tu et al, 2018;. In line with the hypothesized potential of VNS to alter motivational processes via dopamine signaling, we recently found that taVNS affects the learning rate in a go/no-go taVNS increases vigor Neuser et al 5 reinforcement learning task (Kühnel et al, 2019). Thus, non-invasive taVNS may provide a novel and effective means to study the endogenous regulation of motivation according to homeostatic needs.…”

“…Furthermore, vagal afferents regulate learning and memory via hippocampal modulation in rats suggesting a role in reward seeking (Suarez et al, 2018). Likewise, we have observed that non-invasive VNS changes instrumental action learning in humans (Kühnel et al, 2019). Within the feeding circuit, the NTS serves as a hub relaying metabolic information to the mid-and forebrain (de Lartigue, 2016;Grill & Hayes, 2012) including to dopaminergic neurons in the substantia nigra Han et al, 2018).…”

“…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 (Kühnel et al, 2019). Since the default stimulation protocol of the NEMOS taVNS device alternates between 30s 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.…”

Non-invasive stimulation of vagal afferents reduces gastric frequency

“…The electrode was placed at the left cymba conchae (taVNS) or was turned upside down and placed at the earlobe (sham). Prior to each measurement, the stimulus intensity was individually adjusted based on subjective pain thresholds using concurrent VAS ratings [3]. As recommended by the manufacturer, the intensity was increased from 0.1 mA in 0.1 mA increments until participants reported a "tingling" sensation (which was supposed to not be painful).…”

Non-invasive stimulation of vagal afferents reduces gastric frequency

“…Next, we placed the taVNS device on the participants' left ear according to the randomization protocol. The individual stimulation intensity was adjusted based on subjective pain thresholds using concurrent VAS ratings (for details, see [20]). We then recorded at least 30 minutes of EGG and calorimetry during active stimulation before the participant was debriefed.…”