Abstracts

Increased insight into the ictal phenomena that occur in epilepsy, such as the characterization of dynamic regimes during status epilepticus, adds to the store of knowledge of abnormal brain behavior and may assist in improved patient care, including appropriate seizure termination paradigms.
We present a detailed quantitative analysis of ictal phenomena in four patients suffering from a non-convulsive status epilepticus (SE), in whom the EEG shows burst-like patterns of epileptiform discharges (durations 2-30 s) punctuated by low-voltage [apos]flat periods[apos] with a duration of 1-60 s., Epileptiform burst-like transients were identified from the power envelope of the EEG signal. Subsequently,
correlations between initial phases of all possible combinations of the epileptiform burst-like transients were determined. In addition, histograms of the durations of the ictal events and the interictal periods were created. Quantitative analysis of burst duration and inter-burst intervals was performed by evaluation of the distribution of the burst durations and inter-burst intervals. Given the assumed nonlinear nature of the ictal state and the discrete nature of the bursts and the IBI, potential power law behavior was studied., Histograms of the duration of the epileptiform discharges showed a power-law (n=2) or bimodal (n=2) distribution of burst durations, with power-law behavior for the inter-burst intervals, with slopes between -1 and -2 , suggesting the presence of type III or on-off intermittency.
Analysis of the epileptiform bursts indicates the presence of different, isolated brain states (bursts), that often recur in time (45-99% recurrence rate). Figure 1 illustrates the morphology of various pairs of recurrent epileptiform discharges. Left (A-C): data from patient G and Right (D-F) from patient W. The initial portions of the pairs of traces shown are similar, with divergence of later waveforms (red and blue, respectively). These tracings illustrate qualitatively the sensitive dependence on the initial conditions, - one of the characteristics of nonlinear systems., The presence of intermittency and the power-law distribution of the inter-burst intervals during non-convulsive status epilepticus are indications of nonlinear dynamics. Bursts of epileptiform discharges during a non-convulsive SE are manifestations of intermittency with multiple, recurring, brain states.[figure1],