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Zusammenfassung:
To ensure survival, motivated behavior requires to keep expenditure of effort and metabolic costs of actions in balance. The vagus nerve plays a key role in supporting this balance by relaying information on the metabolic state of the body between the gut and the brain. Whereas stimulation of the vagus nerve has been shown to improve aberrant motivational processing in mental disorders such as depression, the neurobiological mechanisms remain largely elusive in humans. Here, we assessed if transcutaneous vagus nerve stimulation (tVNS) affects motivation to work for rewards as well as associations with changes in energy metabolism. We applied tVNS versus sham stimulation in 41 healthy overnight-fasting participants while they completed an effort allocation task (randomized crossover design). A subsample (N=19) underwent two additional sessions of simultaneous electrogastrogram (EGG) and indirect calorimetry under tVNS versus sham. Behaviorally, tVNS increased invigoration for food rewards, but not monetary rewards (p =.005). Physiologically, tVNS reduced gastric myoelectric frequency (p =.038) but did not alter resting energy expenditure (p>.5). Reductions in gastric frequencies were not correlated with task behavior. To summarize, tVNS increases vigor to work for food rewards. The specificity for food rewards suggests that tVNS-induced effects via the nucleus tractus solitarii alter domain-specific dopaminergic neural populations. Moreover, via this mechanism, tVNS may elicit downstream effects on energy metabolism. We conclude that tVNS affects key systems linked to reward processing and energy metabolism, highlighting the potential application of tVNS in targeted treatments for mental disorders with aberrant reward processing.
