Abstracts

RATIONALE: Recent studies indicate that methods derived from the theory of nonlinear dynamical systems extract useful information from the EEG for a spatio-temporal characterization of the epileptogenic process. In previous studies we have shown that increased values of the fraction of nonlinear determinism (?) allow the interictal localization of the primary epileptogenic area in patients with focal epilepsies of different cerebral origins. Here we investigate whether temporal changes of ? calculated from EEG recordings within the focal area are related to an impending seizure. METHODS: The measure ?, which is based upon a combination of the methods of coarse grained flow average and surrogate time series, aims at a discrimination of nonlinear deterministic and linear stochastic dynamics. Intracranial EEG recordings of up to now ten patients with focal epilepsies were analyzed. Using a moving window technique, ? was calculated from recordings of twelve seizures (pre-seizure recording time at least 20 min.) and from recordings during the interictal state (30-120 min. per patient). Values of ? were averaged over recording sites covering the focal area (as confirmed by post-operative complete seizure control) and temporal changes were analyzed. RESULTS: When compared to average values obtained for the interictal state, ? exihibited increased values prior to seven out of twelve seizures while decreased values were found for the remaining seizures. In addition, short- and long-term increases were observed throughout the interictal state which were not followed by a seizure. CONCLUSIONS: Data suggest that a prediction of epileptic seizures based solely on the measure ? is possible only at a weak degree of specificity and sensitivity. Further studies will be necessary to investigate whether a combination with other measures derived from the theory of nonlinear dynamical systems might enhance this performance. [Supported by the Deutsche Forschungsgemeinschaft]