Editorial for the in focus issue of Seizure—European Journal of Epilepsy on “Diagnostic and therapeutic use of invasive electrodes in epilepsy—A “highway” to personalized epilepsy treatment”

The presurgical investigation process of patients hoping to benefit from epilepsy surgery needs to define what to resect and what to spare in order to render a patient seizure free without causing unacceptable neurological deficits. The “neuroimaging revolution” of the last decades has dramatically increased our ability to analyze the brain and its sub-compartments visually and using automated image analysis tools in vivo. The use of these methods often allows us precisely to define brain lesions that may be epileptogenic and the larger structural and functional networks to which they belong. However, we usually need additional electrophysiological data to define the functional relevance of any structural abnormalities for the patient’s epilepsy and to personalize their treatment. Electrophysiological data are indispensable in order to determine the extent and boundaries of the irritative zone, the seizure onset zone, eloquent cortex, and ultimately to generate a hypothesis regarding the location of the epileptogenic zone, which needs to be resected, disconnected, ablated or modified to cure epilepsy [1]. In this respect, invasive electrode (IE) recording contacts placed in or on the surface of the brain, are one of the most important tools in epilepsy surgery, improving precision in diagnosis and treatment. In this “In Focus” edition of Seizure, based on the 7th International Epilepsy Colloquium in Marburg, Germany, we provide an overview of the highly diverse diagnostic and therapeutic uses of IE today. Reif et al. [2] describe the historical development of IE from their initial use by pioneers such as Förster, Penfield and Bancaud. Starting with the intraoperative electrical stimulation of the brain, aiming to define the functional anatomy of the human brain, they moved on to continuous recordings from the surface and depth of the brain using chronically implanted grid and stereo-EEG electrodes. These efforts dramatically improved the spatial resolution of the definition of irritative and seizure onset zones as well as of eloquent cortex, and have allowed us to tailor