Phase synchronization within and between brains during the preparatory period of metronome tempo setting. (A) Topological distributions of PLI in a representative pair of guitarists, A and B, at the theta frequency (4.95 Hz) 140 ms after stimulus-onset (second metronome beat). Fronto-central maxima of PLI are shown. (B) Time-frequency diagrams of average PLI for guitarist A and B separately. PLI was averaged across six fronto-central electrodes. Only significant PLI-values (p < 0.01) are highlighted. Time zero is time locked to the second metronome beat. Metronome beats are shown by white arrows. The time course of PLI values at the theta frequency (4.95 Hz) is depicted below the time-frequency diagram. (C) Interbrain synchronization between the two guitarists measured by IPC at the theta frequency (4.95 Hz) 140 ms after stimulus onset. Colored lines indicate synchrony between electrode pairs of the two guitarists, corresponding to significant interbrain synchronization. Only IPC values higher than 0.41 are highlighted. (D) Time-frequency diagram of the average IPC averaged across six electrode pairs. In the left diagram (A -> B), the selected electrode pairs represent phase coherence between one electrode of guitarist A (Cz) to the six fronto-central electrodes of guitarist B. Conversely, the right diagram (B -> A) refers to one electrode of guitarist B and the six fronto-central electrodes of guitarist A. Only significant IPC-values (p < 0.01) are highlighted. The time course of IPC values at the theta frequency (4.95 Hz) is depicted below the time-frequency diagram. SL = significance level.