A decreased ability of the brain to retain suffi ciently its autonomous dynamics during stimulation can be indicative for pathological neurological conditions, such as epilepsy. Sensory as well as direct brain stimulation can be therefore valuable supplementary tools for identifi cation of suspected epileptic disorders and even for localization of epileptic tissue in the brain. While most stimulation-based approaches rely on spectral or amplitude analysis we argue that important information is contained in the phase clustering index (PCI) derived from the evoked responses to relatively high-frequencies stimulation (>10 Hz) . We present examples where visual sensitivity can be detected by phase-related features of the visual evoked potentials. We also present analysis from intracranial recordings and direct electric stimulation in patients undergoing pre-operative video/EEG. Our results support the hypothesis that the patient’s brain occupies states of increased probability of an epileptic transition prior to seizure. Detection of these states can be relevant as an early warning paradigm. We were also able to fi nd a correlate between the same features of the electrically evoked responses and the location of the seizure onset in cases of localization related epilepsies. We argue that stimulation allows revealing features that are sometimes undetectable by passive observation techniques.
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