Frontal theta power prospectively associated with response inhibition.

A proactive mechanism has been postulated to promote successful inhibition. Specifically, this mechanism is thought to operate before any action-demanding or countermanding event has occurred. In the current study, we investigated whether theta-range oscillatory power measured using electroencephalography (EEG) could reflect this mechanism in a sample of healthy individuals performing a stop-signal task. We tested whether frontal-midline (FM) theta power preceding failed versus successful stop trials predicts inhibition success. Results from two experiments demonstrate that FM theta is indeed higher preceding successful stopping events than failed ones. However, theta power turned out to be equally stronger preceding slow than fast, go trials, suggesting that proactive slowing could explain the association between theta and stop success. There was no correlation between the strength of the within-subject theta-stop-success association and the within-subject theta-RT association. In sum, group-average-level analysis suggests strong overlap between FM theta associated with proactive inhibition and proactive slowing, respectively, while at the same time there are dissociations in terms of individual differences. A further, unexpected, finding was that FM alpha power was specifically associated with proactive inhibition but not with slowing, and, relative to theta, peaked closer in time to the action-demanding event.