The main aim of this study is to evaluate the contribution of fast-ripples (FR) information on the neurosurgery management of patients with drug-refractory epilepsy investigated by Stereo-ElectroEncephaloGraphy (SEEG), as measured by freedom from disabling seizures one-year post-surgery.

220 patients (for whom 4-6 usual clinical macro-electrodes will be replaced by hybrid micro-macro electrodes and for whom fast-ripples will be assessed) distributed over 5 centres and 220 control patients(who will undergo an SEEG with the usual electrodes and for whom fast-ripples will not be assessed) distributed over 6 centres. This is a controlled, non-randomized, parallel plan, prospective, multicentre exploratory study.

This is a controlled, non-randomized, parallel plan, prospective, multicentre exploratory study. The design of the study relies on two groups of patients benefiting from a SEEG, equivalent in size: one with standard and hybrid electrodes for which fast-ripple information will be available for the neurosurgery decision, the other, who will serve as a control group, with standard electrodes only and for which no information regarding fast-ripples will be provided. For all patients undergoing SEEG, the decisions about eligibility to epilepsy surgery and, if eligible, about the best surgical plan, are taken during a multidisciplinary epilepsy meeting (MEM) within the 4 +/- 2 months following the SEEG. In the group of patients with standard and hybrid electrodes, the procedure as extensively tested previously, is to plan the implantation of the standard electrodes as usually done, and once done, to replace from 4 to 6 standard electrodes with hybrid electrodes. In this group, intracerebral ElectroEncephaloGraphy (EEG) data will be acquired for detection of fast-ripples, during one hour of a rest period for 2 days during the first week of SEEG, as well as during one cycle of night sleep when possible. Fast-ripples(number, localization and characteristics) for all these patients will be analysed by an expert group of neuroscientists based in Toulouse blind to the analysis of the Epileptogenic Zone (EZ), irritative and propagation zones and on all micro- and macro contacts, to the participating centre and to the period of recording. The results of the fast-ripple assessment will be provided to the clinicians on time for the MEM. They will incorporate this information along other usual clinical information gathered during the SEEG to reach a conclusion regarding the possibility of a neurosurgery. No analysis of the fast-ripples will be performed in the other group of patients with standard electrodes only. In this group, the conclusion regarding the possibility of a neurosurgery will thus be done during the MEM with the standard clinical information gathered during the SEEG only. Following epilepsy surgery, the typical follow-up performed in routine in all participating centres includes a clinical evaluation one year after surgery, during which Engel class is assessed.

Inclusion Criteria:

• Patient suffering from drug-resistant focal epilepsy (DRFE), as defined by the International League Against Epilepsy, undergoing SEEG, the indication of which was selected during a multidisciplinary epilepsy meeting
• Patient who has given written informed consent to allow the study data collection procedures
• Patient covered by the French healthcare system.

Exclusion Criteria:

• Patients under juridical protection (authorship, curators or safeguarding of justice).
• Patient deprived of liberty by a judicial or administrative decision
• Patient with a cardiac defibrillator
• Thermocoagulation planned on one of the potential hybrid electrodes .
• Patient in exclusion period of another study.
• No other non-inclusion criteria since the study will only be proposed to patients who already meet the criteria for a SEEG