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Abstract

Probabilistic learning is a fundamental mechanism of the brain, which extracts and represents regularities of our environment enabling predictive processing during perception and acquisition of perceptual, motor, cognitive, and social skills. Previous studies showed that the frontal cortex and frontostriatal networks play a critical role during probabilistic learning. Also there is evidence that the functional connectivity between the frontal cortex and posterior brain areas was related to the performance in this fundamental learning mechanism, especially in theta (4–8 Hz) frequency: weaker connectivity between these brain areas was associated with better learning. However, the direction of causality remains unclear. To address this question we aimed to induce theta frequency oscillations of the frontal cortex to test if that enhances probabilistic learning.

We used the Alternating Serial Reaction Time (ASRT) task to measure probabilistic learning. Twenty healthy young adults participated in our study in within subject design. They completed three sessions of the learning task in three conditions, one week apart from each other. During the first twenty minutes of the task they received 1 mA transcranial Alternating Current Stimulation (tACS) with theta or alpha frequency, or sham stimulation bifrontally (F3, F4). All participants underwent all three types of stimulation. The order of the conditions was counterbalanced between participants.

Our study demonstrates the role of the prefrontal cortex in probabilistic learning, and also clarifies the causal relations between brain activity and learning performance.