Abstracts

Dynamic Systems analysis has been applied to the study of interictal and ictal EEG data for more than a decade. Abnormalities in these measures have been reported in the detection, prediction and localization of seizures. The purpose of this study is to extend these observations to the pediatric population, to compare ictal data to three forms of baseline data and to describe some of the features of the spatial distribution of the systems changes, for multiple metrics. Intracranial and extracranial recordings were obtained from a series of pediatric aged patients undergoing evaluation for surgical treatment. Ages varied from 5 to 19 years of age. Three examples of seizures, interictal sleep, interictal awake and preictal (within one minute of seizure onset) were selected and analyzed for each patient. Metrics were calculated for correlation dimension (least squares), correlation dimension (maximum likelihood), Kolmogorov entropy, eigenvalues and Z (a global measure of nonlinearity) in each case. These metrics were calculated for at least eight surface electrodes (four over each hemisphere) and for at least 16 intracranial electrodes. The intracranial electrodes were further subdivided into [quot]involved[quot] versus [quot]uninvolved[quot] in the ictal event according to visual analysis. These data were subjected to analysis of variance and chi square analyses. Eighty percent of the ictal events were detectable. Differences were seen between sleep and wakefulness baselines for 70% of the the group. Preictal changes were seen for 40% of the group, compared to baseline. Seemingly uninvolved electrodes show changes in these metrics both ictally and interictally. The magnitude of the change and the metris showing the changes varied across patients but eigenvalue was most commonly changed amongst the measures. Eigenvalue and correlation dimension (least squares) were the least specific spatially, while Kolmogorov entropy and Z were the most spatially specific. We continue to observe ictal changes in dynamic systems measures in pediatric aged patients with seizures. The measures are also abnormal in a number of patients interictally. No single metric is complete enough to stand alone, from a detection or anticipation perspective. Anticipation was possible in nearly half of the cases. The most surprising findings of this study were that electrodes felt to be [quot]control[quot] or uninvolved in the seizures can show significant changes in these metrics and that the metrics vary considerably in their spatial specificity. Localizing a focus using these metrics must be performed with considerable caution. Further, the differences in spatial distribution across metrics suggest that these metrics do not all reflect the operation of a single process. (Supported by Falk Medical Trust Foundation.)