Quantification of phase synchronization phenomena and their importance for verbal memory processes.

In the past years, interest in brain oscillations and their possible role in perceptual and cognitive processes has greatly increased. The two oscillations that have received the most attention are the theta and the gamma rhythm. In this study, the functioning and properties of phase synchronization parameters for these two frequency bands estimated by means of Gabor expansion were demonstrated with simulations for the phase-locking index (PLI) and the 1:1 as well as n:m phase synchronization indices. In order to demonstrate the importance of phase synchronization phenomena for memory performance, power, PLI and the 1:1 as well as n:m phase synchronization indices were calculated for EEG data on verbal memory encoding. These parameters showed various dissociations for recalled versus not-recalled nouns. In particular, the calculation of phase synchronization among different frequencies either at the same electrode or at different electrodes provided a completely new picture of dynamic neuronal interaction accompanying memory processing.