Single-trial EEG power and phase dynamics associated with voluntary response inhibition.

Human voluntary response inhibition has frequently been investigated using go/no-go RT tasks. Recent studies have indicated that not only the traditional averaging waveforms of EEG activities (ERPs) but also the power and phase dynamics of single-trial EEG are important in studying the neural correlates of various human cognitive functions. Therefore, here, we aimed to undertake a detailed study of the time/frequency power and phase dynamics of single-trial EEG during go/no-go RT tasks, with focus particularly on the no-go-specific power and phase dynamics, which are presumed to involve the voluntary response inhibition processes. Thus, we demonstrated no-go-specific theta band EEG power increases and intertrial phase-locking in the midline-frontal areas, which are related to no-go-specific midline-frontal negative-positive ERP waveforms (no-go N2/no-go P3). In addition, we observed no-go-specific alpha band EEG intertrial phase-locking with an adjacent dephasing phenomenon, which is mainly associated with the early part of no-go N2. The estimated time point when the no-go-specific midline-frontal dephasing phenomenon occurred corresponded to the initial part of the voluntary response inhibition process (decision to withhold). Moreover, the no-go-specific phase dynamics in the midline-frontal areas just before and around the no-go N2 peak latency, unlike the power modulations, were affected by changes in the no-go stimulus probability, suggesting the dependence of only phase dynamics on no-go stimulus probability. From these results, we conclude that the complex power and phase dynamics of the theta and alpha band EEG in the midline-frontal areas are specific to no-go trials, being the underlying bases of the no-go-specific ERP waveforms, and suggest that the phase dynamics just before and around the no-go N2 peak latency may involve, at least, the initial part of the voluntary response inhibition process (decision to withhold).