Backward alpha band oscillations shape perceptual bias under probabilistic cues

Predictive coding theory suggests that prior knowledge is crucial for optimizing human decision-making. However, how cortical dynamics implement this integration remains unclear. Here, we employ a traveling wave approach to investigate how alpha band oscillations integrate prior expectations during a perceptual decision-making task. Our findings demonstrate that expectation-based knowledge triggers the propagation of alpha band 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 rely more on prior expectations exhibit stronger top-down signaling (frontal-to-occipital), whereas those who focus on sensory input show a contrasting bottom-up pattern (occipital-to-frontal). 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. Alpha-band traveling waves carry predictive signals across the cortex. Backward waves encode prior expectations and tune sensory processing, revealing how individual brains integrate predictions during perceptual decisions.