Non-invasive vagus nerve stimulation boosts mood recovery after effort exertion

Fig. 1.. Experimental procedure and schematic summary of the task block. The timeline shows the experimental procedure with stimulation beginning before a block of three tasks. State measurements were taken before stimulation, during stimulation as well as after the tasks, and after stimulation using visual analog scales (VAS). The food cue reactivity task required quick ratings of wanting and liking. The effort allocation task required physical effort to obtain rewards by pressing a button vigorously. The reinforcement learning task required cognitive effort to track which actions following a cue maximize reward and minimize punishments.

Fig. 2.. Transcutaneous auricular vagus nerve stimulation (taVNS) increases positive mood in the post-stimulation visual analog scales (Run 3). (a) No significant changes in a negative mood. (b): Significant increase in positive mood 20 min post-stimulation (light gray shading), but not during stimulation (gray shading). Error bars denote 95% confidence intervals derived via bootstrapping. (c): Posterior distribution of the taVNS-induced change in a positive mood (95% credible interval in light blue, median in dark blue). BF10 = Bayes factor for the alternative hypothesis.

Fig. 3.. Lower positive mood at baseline is associated with greater improvements in invigoration induced by transcutaneous auricular vagus nerve stimulation. (a) Scatter plot of positive mood ratings at baseline and taVNS-induced changes in invigoration during the acute stimulation phase. (b) Evidence for the alternative and the null hypothesis given the observed association. BF10 = Bayes factor for the alternative hypothesis.

Fig. 4.. Changes in positive mood ratings during the post-stimulation effects are invariant across stimulation sides and items. (a) Changes in positive mood relative to baseline are depicted for each participant (dots) and as group density. Changes are comparable for transcutaneous auricular vagus nerve stimulation (taVNS) applied to the left and the right side. (b) Changes in positive mood relative to baseline are largely invariant across items indicating a general effect of taVNS on mood.