The dissociation in timing between trial-averaged theta – which had a narrow peak 100 ms (power) and 122 ms (cross-trial phase coherence) prior to the response – and the single-trial theta response time regression coefficients – which started earlier and peaked 176 ms before the response (see Figure 9), suggests two distinct but nearly temporally overlapping roles of medial frontal theta dynamics. On the one hand, peri-response theta is involved in general response-locked dynamics; on the other hand, it is the pre-response theta that is tightly coupled to response time. Indeed, medial frontal activity correlating with trial-to-trial RT has been reported previously with EEG independent components analysis (Delorme et al., 2007), and with a re-analysis of five fMRI datasets (Yarkoni et al., 2009). Further, the dissociation between the extended pre-response time course of the theta power regression and the theta phase modulation analysis (compare red and black lines in Figure 10), in combination with the weak pre-response phase coherence (Figure 2D), suggests that reaction time dynamics are more closely associated with non-phase-locked oscillatory activity compared to phase-locked transients. In other
