A METHOD TO QUANTIFY INVARIANT INFORMATION IN DEPTH-RECORDED EPILEPTIC SEIZURES

In the field of epilepsy, the analysis of stereoelectroencephalographi c (SEEG) signals recorded with depth electrodes provides major informa tion on interactions between brain structures during seizures. A metho dology of comparing SEEG seizure recordings is applied in 4 patients s uffering from temporal lobe epilepsy. It proceeds in 3 steps: (i) segm entation of SEEG signals, (ii) characterization and labeling of segmen ts and (iii) comparison of observations coded as sequences of symbol v ectors. The third step is based on a vectorial extension of Wagner and Fischer's algorithm to first, quantify similarities between observati ons and second, extract invariant information, referred to as spatio-t emporal signatures. These are automatically extracted by the algorithm without the need to make a priori assumptions on the 'patterns' to be searched for. Theoretical results show that two observations of non-e qual duration can be matched by deforming the first one (using inserti on/deletion operations on vectors) to optimally fit the second, under a minimal cost constraint. Clinical results show that the study brings objective results on reproducible mechanisms occurring during seizure s: for a given patient, quantified descriptions of seizure periods are compared and similar ictal patterns, or signatures, are extracted fro m SEEG signals. Some of these signatures (particularly those containin g spikes, spike-and-waves, slow waves and rapid discharges) are releva nt: they seem to reflect reproducible propagation schemes whose analys is may help in the understanding of epileptogenic networks. (C) 1997 E lsevier Science Ireland Ltd.