Abstracts

Independent component analysis (ICA) is a system that finds independent sources in many types of signals. One of its capabilities is to study the epileptiform discharges to probe the similar or different origin of its components. The goal of this study was to discover how ICA analyse the spike-and-wave discharges of several types of epilepsies, and to use this information to know more about the origin and propagation of the interictal discharges. We analyzed 60 spikes of 16 patients (3 temporal epilepsy (n=15), 3 centrotemporal (n=15), 4 frontal (n=15) and 6 with generalized epilepsies (n=15)). Most of them were followed by a slow wave (spike-and-wave discharge). The samples were recorded digitally with a 32-channels Lamont amplifiers and Harmonie 5.2b program. ICA was applied using the JADE algorithm implemented in a Matlab platform. The components were identified visually. The suspected components were selected and the EEG of these components by itself and together were reconstructed. The topography in each component of the discharge was compared with the original using the BESA program in the same period. In the focal discharges, ICA separated the spike frorm the wave components, getting a close but not similar topography. The spikes of the focal discharges were separated in one or two components at maximum. The topography of these components was very similar but not identical. Each component of the spike or wave in these focal epilepsies accounted very well for the EEG in the correspondent time.
In the discharges of the generalized epilepsies the patterns were more variable. The spikes were divided in up to 4 components (only in a small percentage in one or two), having very often a variable topographic distribution. The majority of the components were asymmetrical. In the same burst of spike-and-wave discharges, the components of the spikes may vary and even new components may appear. ICA differentiates several components in the epileptiform discharges. In each patient the way of decomposition of the discharge was very similar. In most of the discharges, the spike and the wave had different components suggesting different origin. The generalized discharges had more complexity than the discharges in focal epilepsies, and even in the same patient the variability was higher. (Supported by the UTE project CIMA and by the Government of Navarra, grants for research in Health 12/2003 and 16/2003. Dr Urrestarazu is a Research Fellow supported by a grant for research of the Department of Education of the Basque Government.)