Abstracts

Rationale: Approximately half of the patients with a diagnosis of pharmaco-resistant epilepsy are potential candidates for epilepsy surgery. In 30-40% of drug-resistant patients with focal epilepsy the cerebral areas responsible for seizure generation can only be defined by intracranial recordings. The correct pre-surgical identification of the epileptogenic zone with intracranial recordings has a direct impact on post-surgical outcome. At present, the identification of the epileptic zone is based on visual inspection of the intracranial EEG. One of the principal impediments to computer-driven analysis of intracranial signals is the complexity and the quantity of data recorded during pre-surgical stereo-EEG sessions. Methods: A new method for stereo EEG analysis was developed to retrospectively evaluate pre-surgical intracranial recordings in patients with pharmaco-resistant partial epilepsy. StereoEEG data were exported to a program developed in LabView for elaboration. Prevalent frequencies during seizure events were evaluated by Fourier transformation and further integral algorithms. Different frequencies and the relative powers were simultaneously evaluated in all recording leads. Patterns characterized by specific and prevalent frequencies were identified in a subset of recording sites during both seizure onset and seizure development. 3D-maps of the measurements obtained from each recording channels were reconstructed on magnetic resonance coordinates to visualize the spatial distribution of the analyzed contacts. Results: Fast activity at 20-40 Hz was typically observed at the onset of seizures and during interictal period. During seizures a faster activity (50-250 Hz) of lower voltage, coupled with a very slow wave deflection was observed. The clinical correlates of these patterns were also analyzed. Seizure termination was characterized by a recovery of fast activity at 20-40 Hz that in most cases evolved into high amplitude bursts separated by brief EEG flattenings. Conclusions: The present report describes a new computer-assisted method developed to analyze intracranial EEG traces. With this method, the reproducibility of ictal patterns in the same patient was characterized and the spatial distribution of specific StereoEEG signals associated with different types of seizures was recognized. In addition to the obvious clinical and diagnostic implications, the use of quantified analysis of intracranial EEG signals recorded directly into seizure generators could contribute to understand the neurobiological mechanisms responsible for the initiation and the propagation of focal seizures in humans. The study was sponsored by a Mariani Foundation grant R-08-71 and by the Italian Ministry of Health Young Investigator Grant 2007.