Transcutaneous Vagus Nerve Stimulation Enhances Probabilistic Learning.

tVNS enhances various memory and learning mechanisms, but there is inconclusive evidence on whether probabilistic learning can be enhanced by tVNS. Here, we tested a simplified version of the probabilistic learning task with monetary rewards in a between-participants design with left and right-sided cymba conchae and tragus stimulation (compared to sham stimulation) in a sample of healthy individuals (n = 80, 64 women, on average 26.38 years old). tVNS enhances overall accuracy significantly (p = 4.09 x 10^-04) and reduces response times (p = 1.1006 x 10^-49) in the probabilistic learning phase. Reinforcement learning modelling of the data revealed that the tVNS group uses a riskier strategy, dedicates more time to stimulus encoding and motor processes and exhibits greater reward sensitivity relative to the sham group. The learning advantage for tVNS relative to sham persists (p = 0.005 for accuracy and p = 9.2501 × 10^-27 for response times) during an immediate extinction phase with continued stimulation in which feedback and reward were omitted. Our observations are in line with the proposal that tVNS enhances reinforcement learning in healthy individuals. This suggests that tVNS may be useful in contexts where fast learning and learning persistence in the absence of a reward is an advantage, for example, in the case of learning new habits.