Event-related spectral perturbations and phase synchronization of EEG during natural auditory memory retrieval task

Brain oscillations and connectivity have received considerable attention in cognitive neuroscience. In this study, we recorded the electroencephlography (EEG) signals of thirteen subjects recruited for the natural auditory memory retrieval task. EEGs were recorded using an electrode cap with event-related potentials (ERPs) and event-related spectral perturbations (ERSPs) computed. For evaluating the interaction between distinct brain regions, phase-locking value (PLV) was calculated to determine the functional connectivity for distinct frequency bands. The results of ERSPs show that there is larger delta (1-4 Hz) and theta (5-8 Hz) synchronization in the left- and midline-frontal areas for subjects when they attend to the music segments with main theme. For the desynchronization of the alpha oscillation (8-12 Hz) in the midline-occipital and parietal region, the local suppression may indicate the engagement of specific cortical areas in sensory or cognitive functions. There is also strong beta synchronization when the subjects were attending to melody similar to the main theme which may indicate the active inhibition of motor cortices. The functional connectivity is shown by calculating the phase synchronization. Since the task is mainly related to the retrieval of working memory, the phase-locking value for the theta band is significantly larger when the subjects heard the melody similar to the main theme than the condition without main-theme recognition. However, the difference of phase synchronization between main-theme condition and other sound segments is not significant. The phase synchronization is significantly larger for the condition of similar melody in the frontal-parietal, frontal-temporal, and temporal-parietal regions which may indicate the processing of memory information.