Characteristics of spontaneous anterior-posterior oscillation-frequency convergences in the alpha band

Alpha oscillation frequencies vary along the anterior-posterior axis, but they also dynamically converge. We investigated spontaneous anterior-posterior oscillation-frequency convergences while participants rested with their eyes open or closed, by tracking their oscillatory EEG activity in an extended alpha range (5-15 Hz) with appropriate temporal ({bsim}370 ms) and spectral ({bsim}1 Hz) resolutions. Oscillation-frequency convergences were prominent in the alpha band (8-12 Hz) and our analyses revealed three primary characteristics. First, the probability of an additional site joining a frequency convergence increased as more sites frequency-converged, suggesting that synergistic interactions drive anterior-posterior frequency convergences. Second, the oscillatory power at participating sites increased as more sites frequency-converged, suggesting that the synergistic interactions are mediated by regional synchronizations, being boosted by inter-regional frequency matching, facilitating the entrainment of additional regions. Third, frequency convergences generated two opposing phase gradients, posterior-behind and posterior-ahead, potentially mediating directional information flows to and from posterior regions. These gradients became steeper as more sites frequency-converged (while maintaining relatively constant levels of phase consistency), suggesting that frequency convergences increase the directionality of anterior-posterior information flows. Interestingly, when participants closed their eyes, the opposing phase gradients spatially organized, forming posterior-ahead gradients along the midline and posterior-behind gradients within each hemisphere, suggesting that closing eyes streamlines the opposing information flows. Taken together, these results suggest that synergistic interactions drive spontaneous anterior-posterior oscillation-frequency convergences in the alpha band, which may contribute to directional flows of information to and from posterior regions.