Theta-gamma phase synchronization during memory matching in visual working memory.

In most cases, object recognition is related to the matching of internal memory contents and bottom-up external sensory stimulation. The aim of this study was to investigate the electrophysiological correlates of memory matching based on EEG oscillatory phase synchronization analysis. Healthy subjects completed a delayed-match to sample task in which items stored in visual-spatial short-term memory had to be compared with a matching or non-matching probe. The results show that memory matching appears as transient phase-synchronization over parieto-occipital regions between theta (4-8 Hz) and high gamma (50-70 Hz) oscillations, 150-200 ms post probe presentation. When memory representation and visual information match, phase-synchronization is stronger in the right hemisphere; conversely, when they do not match, stronger phase synchronization is observed in the left hemisphere. The present results reveal the integrative role of oscillatory activity in the memory matching process. Copyright 2010 Elsevier Inc. All rights reserved.