Spontaneous and electrically-induced cortical excitability changes of epileptic networks after radio-frequency thermo-coagulation

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Epilepsy is a network disease. Epileptic activity travels fast though the brain and even in focal epilepsies inter-ictal epileptic activity can involve widespread brain regions. Epileptic brain show sign of permanent widespread changes but despite these observations patients become seizure free after focal resections of the seizure onset. It is therefore likely that a focal generator of epileptic activity is part of a larger epileptic network, and interacts with physiological brain activity, the extent and clinical relevance of this phenomenon however is poorly understood. RFTC (Radiofrequency thermocoagulation) during chronic. Stereotactic intracerebral EEG (SEEG) recordings is a new minimally invasive treatment for patients with refractory epilepsy. It can be used to try to eliminate a seizure focus during the chronic SEEG investigation. In the context of focal and widespread epileptic network interactions this treatment provides the unique opportunity to assess changes in epileptic networks with intracerebral EEG after ablation of the epileptic focus and correlate these changes with seizure outcome. High frequency oscillations (HFO) between 80-500Hz are described during physiological processes such as memory consolidation and as new focal markers for epileptic tissue. Retrospective studies suggest that the removal of HFO generating tissue correlates with the postsurgical seizure outcome. Nevertheless a prospective study from our center indicates that HFO identified presurgically during intracerebral EEG recordings do not allow predicting seizure outcome in individual patients. Acute intraoperative intracranial EEG recordings allow comparing HFO networks prior and after surgery and suggest that the postsurgical measurement of HFO are more reliable in predicting postoperative seizure outcome. Moreover cortico-cortical evoked potentials can be used to probe epileptic networks and assess evoked HFO. This collaborative project between the Epilepsy Centers in Grenoble, France and Freiburg, Germany patients will differentiate between physiological and epileptic HFO using correlation analysis with sleep pattern. Changes in CCEP (cortico-cortical evoked potentials) network and regional spread of epileptic HFO and epileptic spikes will then be analyzed prior and after RFTC intervention. The following hypothesis will be tested: 1) Isolation of the epileptic focus by RFTC can be measured by a reduction of epileptic HFO and reduced cortical excitability as measured with CCEP, 2) Post-interventional HFO and CCEP analysis may be used to improve prediction of post-interventional seizure outcome, 3) In patients which fail to profit from RFTC remaining HFO networks and information from high frequency activity during CCEP help to predict seizure outcome after the consecutive resective surgery.