The more we anticipate a response to a predictable stimulus, the faster we react.
This empirical observation has been confirmed and quantified by many investigators
suggesting that the processing of behaviorally relevant stimuli is facilitated by
probability-based confidence of anticipation. However, the exact neural mechanisms
underlying this phenomenon are largely unknown. Here we show that performance changes
related to different levels of expectancy originate in dynamic modulation of delta
oscillation phase. Our results obtained in rhythmic auditory target detection tasks
indicated significant entrainment of the EEG delta rhythm to the onset of the target
tones with increasing phase synchronization at higher levels of predictability. Reaction
times correlated with the phase of the delta band oscillation at target onset. The
fastest reactions occurred during the delta phase that most commonly coincided with
the target event in the high expectancy conditions. These results suggest that low-frequency
oscillations play a functional role in human anticipatory mechanisms, presumably by
modulating synchronized rhythmic fluctuations in the excitability of large neuronal
populations and by facilitating efficient task-related neuronal communication among
brain areas responsible for sensory processing and response execution.
