Alpha oscillations shape sensory representation and perceptual sensitivity

Alpha oscillatory activity (8 - 14 Hz) is the dominant rhythm in the awake brain, and is thought to play an important role in setting the brain9s internal state. Previous work has associated states of decreased alpha-band oscillatory power with enhanced neural excitability. However, opinions differ on whether and how such excitability enhancement modulates sensory signals of interest versus noise differently, and what, if any, the consequences are for the subsequent perceptual process. To address these questions, we used a novel paradigm to experimentally manipulate human subjects9 decision criteria in a visual detection task. In different blocks, we primed subjects with clearly visible stimuli to introduce either a liberal or conservative detection criterion for subsequent ambiguous stimuli. While we observed substantial criterion shifts under different priming conditions, such criterion shifts were not reflected in pre-stimulus alpha-band changes. Rather, we found that lower pre-stimulus alpha-band power in early visual cortices improved perceptual accuracy, accompanied by enhanced information content decodable from the neural activity patterns. Additionally, we showed that alpha oscillatory phase in parietal and frontal regions immediately before stimulus presentation modulated accuracy. Together, our results suggest that alpha-band dynamics modulate sensory signals of interest more strongly compared to noise, here resulting in enhanced information coding and improved perceptual accuracy.