Reduced signal complexity of intracellular recordings: a precursor for epileptiform activity?

Recent studies have shown that time windowed extraction of nonlinear parame ters like an effective correlation dimension from intracranially recorded E EG of epileptic patients often allows to detect and identify an unequivocal "pre-ictal phase" preceding an epileptic seizure. In another study, howeve r, such an anticipation could not be made. These conflicting findings may i ndicate that observed changes in nonlinear parameters probably depend on th e type of elementary mechanisms underlying epileptic processes and/or the s patial distribution of neurons primarily involved in generation of epilepti form discharges. To test the existence of such dependencies, the transition from normal to epileptiform activity (EA) of CA3-neurons in hippocampal sl ices was analyzed in four epilepsy models, using a time windowed computatio n of an effective correlation dimension. Indeed, in xanthine and penicillin models, signal complexity in intracellular recordings was reduced before m anifestation of paroxysmal depolarization shifts (PDS), whereas a preceding loss of complexity was missing in low-magnesium and veratridine models. Th ese findings indicate that interictal-like EA is predictable only in some e pilepsy models. (C) 1999 Elsevier Science B.V. All rights reserved.