Abstracts

Rationale: In many epileptic patients, seizures originating from the same focus often produce very similar EEG signals, particularly recorded intracranially. Using information from multiple seizures improves the statistical properties of estimators, allowing for the application of a greater variety of signal processing methods. This may be particularly useful for methods requiring stationary epochs. This may also help in the analysis of seizure propagation and the localization of seizure foci.Methods: The short-time direct directed transfer function (SdDTF) method, recently developed to investigate the directions and intensities of activity flow between cortical regions during cognitive tasks with multiple trials, was applied to intracranial recordings of 5 patients with multiple seizures (N = 5-80). A multichannel autoregressive model (MVAR) was fitted simultaneously to all recorded seizures. The seizures were aligned according to their ictal onsets, judged by visual inspection. Preictal intervals of 60 sec, as well as ictal segments of 60 sec were analyzed.Results: The SdDTF method showed flow of activity from the ictal onset zone. For patients with a large number of seizures (>50), the time resolution was sufficient (~ 0.5 sec) to observe dynamic changes in flow during seizures. During the preictal period significant flow of low frequency activity could be observed in the vicinity of the focus. With fewer seizures the time resolution is lower and fewer channels can be analyzed simultaneously, but flows of large magnitude can still be observed. Conclusions: The improved statistical properties of flow estimates derived from multiple seizures allow for analysis of shorter stationary windows and more appropriate application to changing ictal patterns. The SdDTF method may provide additional information about the dynamics of seizure propagation. Using all available seizures focuses on the features common among multiple seizures. Supported by: NINDS R01 NS40596 and NS48222