The study intends to probe the effect of seizures on cerebral connectivity, both on a local and on a global level. Children who undergo presurgical evaluation to probe whether their epilepsy can be cured by surgery are recorded with implanted intracerebral electrodes for clinical purposes. A diffusion Magnetic Resonance Imaging will be performed prior to implantation in order to relate tractography measures to seizure recordings. On the local level, intracerebral electroencephalogram (EEG) will be analysed to quantify the intensity of epileptic discharge (the epileptogenicity index) on each electrode contact. Loss of connectivity (or disconnections) is determined with diffusion tractography for each brain region. Then correlation between the degree of epileptogenicity and with the number of disconnections will be studied.