Decomposition and mapping of generalized spike-wave complexes

Objective: To delineate more precisely the electrical fields of spikes versus waves during absence seizures. Methods: Five children with 25 absence seizures were investigated with an expanded electrode array. Spikes were separated from waves by appropriate filtering and current source density maps were obtained from different portions of the waves as well as spikes. In order to detect commonalities for spread of activity, averaging of the complexes was also carried out. Results: The anterior head regions (prefrontal and fronto-polar) show independent activity from the posterior ones (parieto-occipital) for spikes as well as waves. Voltage maps give a simplified and therefore misleading picture. The complexity of the process and propagation of events is best appreciated when current source densities (CSD) are mapped and several head views are available. Spike 1 becomes clearly visible upon filtering, even when it is not apparent from raw tracings, and can be mapped. Conclusions: Future topographic investigations of the SW complex should utilize CSD maps rather than rely entirely on voltages. This applies also to seemingly focal spikes – especially in children – in order to differentiate them from a partial expression of a generalized seizure tendency.