The Extent of an Epileptogenic Zone: Application of Signal Processing Methods

Delineation of the epileptogenic zone extent is critical for surgical treatment. Various time-frequency methods have approached this utilizing differing approaches and theoretical perspectives. These will be reviewed and appraised with respect to surgical outcome. The relevance of the seizure-onset patterns/dynamics and the preictal-ictal transition (“fingerprint”), versus the tracking of fast activity, will be emphasized, especially the differentiation between “primary” and “propagated” fast activity. Ictal infraslow activity and late phase-locked high gamma will be considered, demonstrating the localizing value of data beyond seizure onset. Understanding these various features as they relate to “primary organization” and the underlying pathophysiology will be attempted. A case example will be used to illustrate two differing approaches: epileptogenicity index and “fingerprint” prediction of the epileptogenic zone.