Does spatiotemporal synchronization of EEG change prior to absence seizures?

We applied linear and nonlinear synchronization measures to characterize the synchrony between cortical regions and detect cerebral epileptic states in scalp EEG recordings recorded prior and during typical absence seizures. An overall rapid increase in the synchronization level between different cerebral regions was observed during the ictal state. During the interictal state, the degree of interdependence between EEG channels was significantly less than that observed in the ictal state (p<0.05). In 63% of the 35 seizures analyzed, a preictal state was identified by a significant decrease in the synchronization level with respect to the interictal state. However, in 31% of the seizures, the synchronization level in the preictal state was higher than that of the interictal state. In the remaining 6% of the seizures, no significant changes were found in the synchronization values in the interictal state prior to the seizures onset. In all the seizures analyzed, the interchannel synchrony persisted in the postictal state with synchronization level significantly higher than that observed in the interictal state. This study supports the hypothesis of having a focal susceptibility of the cerebral cortex prior to absence seizures and further underlines that this susceptibility is reproducible and patient-specific.