Right hemisphere advantage in statistical learning: evidence from a probabilistic sequence learning task.

BACKGROUND: Picking up statistical regularities of patterns from the environment is essential for predictive and adaptive behavior. One of the most important challenges is to understand how statistical learning occurs and how the acquired information consolidates and stabilizes in the brain. Evidence suggests that the prefrontal cortex (PFC) has a critical role in these processes; the division of labor between hemispheres, however, is less characterized. OBJECTIVE/HYPOTHESIS: The aim of the present study was to directly investigate the causal role of the right and left PFC in statistical learning and its consolidation. METHODS: Healthy, young adults were trained on a probabilistic sequence learning task. Anodal transcranial direct current stimulation (tDCS) over the right or left dorsolateral PFC (DLPFC) was applied during the training in order to modify learning-related cortical plasticity in the targeted brain regions by increasing neural excitability. Performance was tested during and immediately after the stimulation, 2-h and 24-h later. RESULTS: We found that the anodal tDCS over the right DLPFC led to enhanced learning performance both after the 2-h and 24-h retention periods, suggesting the causal role of this area in statistical learning. In contrast, we did not find any effect of left DLPFC stimulation on learning. CONCLUSIONS: These results highlight the role of the right fronto-striatal network in statistical learning and its consolidation.