Backward alpha oscillations shape perceptual bias under probabilistic cues

Predictive coding theory suggests that prior knowledge is crucial for optimizing human decision-making, with recent studies emphasizing the role of alpha-band oscillations in this process. Here, we employed a traveling waves approach to investigate how alpha oscillations integrate prior expectations during a perceptual decision-making task. Our findings demonstrated that expectation-based knowledge triggers the propagation of alpha traveling waves from frontal to occipital areas, with this increase associated with enhanced modulation of brain regions involved in stimulus processing and directly linked to prior-driven bias at the behavioral level. Moreover, participants who relied more on prior expectations exhibited stronger top-down signaling, whereas those who focused on sensory input showed a contrasting forward signaling pattern. These results highlight the role of alpha-band traveling waves in predictive mechanisms, suggesting that rhythmic interactions across brain regions facilitate this process and contribute to inter-individual differences in its implementation.