Nearest neighbor phase synchronization as a measure to detect seizure activity from scalp EEG recordings

The author presents results from the application of a particular measure for synchronization between brain areas (i.e., phase synchronization) in its behavior to detect epileptic seizure activity from scalp EEG recordings. The primary motivation for the current study was to contribute to the development of physiologic measures that both transform the EEG to a visual domain that allows a more intuitive interpretation of the interictal and ictal EEG and allows automated analysis, both relevant for real-time monitoring. EEGs from 16 patients experiencing temporal lobe and generalized seizures were analyzed. Nearest neighbor phase synchronization (NNPS) values for several frequency bands were determined. Additional analysis of the NNPS in the delta band, using different thresholds, allows construction of receiver operating characteristics (ROC) curves for each EEG analyzed. The common value for the sensitivity and the specificity, Q*, was used as a measure for the test accuracy, with values of Q* near 1.0, indicating ROC curves with sensitivity and specificity both approaching 1.0. It was found that Q*=0.48 to 0.87, depending on the EEG analyzed, indicating that the proposed method allows seizure detection in a significant portion of the EEGs studied. Nearest neighbor phase synchronization was typically increased during seizure activity and seems to be a promising method to detect seizure activity from scalp EEG recordings. The proposed visualization allows an intuitive interpretation of the EEG and may assist in real-time monitoring.