Synchronization and clustering in electroencephalographic signals

Two order parameters introduced in the context of coupled chaotic systems subject to external noise are employed to measure the degrees of synchronization and dynamical cluster formation in electroencephalographic (EEG) signals. These parameters are calculated in EEG signals from a group of healthy subjects and from a group of epileptic patients, including a patient experiencing an epileptic crisis. The evolution of these parameters show the occurrence of intermittent synchronization and clustering in the brain activity during an epileptic crisis. Significantly, the existence of an instantaneous maximum of synchronization previous to the onset of a crisis is revealed by this procedure. The mean values of the order parameters and their standard deviations are compared between both groups of individuals.