Fig. 2.

Comparison of phase/amplitude coupling methods. (a) Methods for calculating traditional blocked PAC and event-related PAC (ERPAC) begin similarly: the raw signal is filtered into separate amplitude and phase components (here broadband γ analytic amplitude and α phase). For traditional blocked PAC analyses, a single PAC index is calculated across an arbitrarily long time window at the cost of temporal resolution. (b) To calculate ERPAC, the phase and time series are broken into time windows of equal length around each trial, time-locked to the onset of stimulus presentation (example black rectangles in a). In contrast to blocked PAC, which is calculated across time, ERPAC is calculated across trials separately at each time point. In this example (from the electrode shown in Figure 1), trial-by-trial differences in α phase explain a significant amount of the inter-trial variability in broadband γ amplitude during a brief time window (50-250 ms) after stimulus onset. See Methods for full details.