Increased phase synchronization during continuous face integration measured simultaneously with EEG and fMRI

ObjectiveGamma zero-lag phase synchronization has been measured in the animal brain during visual binding. Human scalp EEG studies used a phase locking factor (trial-to-trial phase-shift consistency) or gamma amplitude to measure binding but did not analyze common-phase signals so far. This study introduces a method to identify networks oscillating with near zero-lag phase synchronization in human subjects.MethodsWe presented unpredictably moving face parts (NOFACE) which – during some periods – produced a complete schematic face (FACE). The amount of zero-lag phase synchronization was measured using global field synchronization (GFS). GFS provides global information on the amount of instantaneous coincidences in specific frequencies throughout the brain.ResultsGamma GFS was increased during the FACE condition. To localize the underlying areas, we correlated gamma GFS with simultaneously recorded BOLD responses. Positive correlates comprised the bilateral middle fusiform gyrus and the left precuneus.ConclusionsThese areas may form a network of areas transiently synchronized during face integration, including face-specific as well as binding-specific regions and regions for visual processing in general.SignificanceThus, the amount of zero-lag phase synchronization between remote regions of the human visual system can be measured with simultaneously acquired EEG/fMRI.

► Using a visual binding task as example, this study presents a method to measure the amount of EEG gamma zero-lag phase synchronization and to locate its underlying regions with fMRI. ► We found an increased amount of gamma zero-lag phase synchronization during FACE compared to NOFACE with positive BOLD correlates in the left and right middle fusiform gyrus and the left precuneus. ► We thus suggest that the difference in gamma band phase between remote regions of the human visual system shifts toward zero during visual binding and can be measured with simultaneously acquired EEG/fMRI.