Stationarity and redundancy of multichannel EEG data recorded during generalized tonic-clonic seizures

To improve our understanding of the physiology of generalized tonic-clonic (GTC) seizures, we have investigated the stationarity and redundancy of 21- electrode EEG data recorded from ten patients during GTC seizures elicited by electroconvulsive therapy (ECT). Stationarity was ex amined by calculati ng probability density functions (pdfs) and power spectra over small equal- length non-overlapping time windows and then by studying, visually and quan titatively, the evolution of these quantities over the duration of the seiz ures. Our analysis shows that some seizures had no demonstrable stationarit y, that most seizures had time intervals of at least a few seconds that wer e statistically stationary by several criteria, and that, in some seizures, there were leads which were delayed in manifesting the statistical changes associated with seizure onset evident in other leads. The redundancy analy sis demonstrated for the first time posterior-to-anterior time delays in th e mid-ictal region of GTC seizures. The implications of these findings are discussed for the analysis of GTC seizure EEG data, for the physiology of G TC seizures, and for ECT research.