The accurate definition of the seizure onset zone (SOZ) is a central problem in drug-resistant epilepsies. Signal processing methods may be used to complement the interpretation of SEEG recordings by quantifying interictal events and SOZ. In this chapter, we will describe some of these methods and focus on insular epilepsies with some detailed case examples.

Insular epilepsy has caught increasing attention in the presurgical evaluation of drug-resistant focal epilepsies, and it is evident that intracranial EEG recordings can be considered the best method to investigate such a deep-seated area of the brain, especially in non-lesional patients. Intracranial EEG recordings allow us to better understand the organization of epileptic EEG discharges involving the insular cortex and the complexity of the relationships between the insula and the different connected regions of the brain, particularly the opercular region. This peculiarity thus explains the heterogeneous clinical presentation of seizures arising from insular or insulo-opercular structures. While most patients have an epileptogenic zone extending beyond the insula, some have very focal ictal insular discharges, allowing the possibility of a restricted surgical resection. Consequently, only an appropriate sampling of the insula and of extra-insular connected structures can permit a precise identification of the epileptogenic zone and planning for a tailored resection.