Abstracts

Evaluating the location and distribution of scalp EEG-recorded interictal epileptiform discharges is an important part of the evaluation of medically refractory localization-related epilepsy. In some cases this information is useful in predicting the zone of seizure onset. This project was undertaken to determine if additional information can extracted from the scalp EEG by employing dense-array (256-channel) EEG, when compared to that obtained by conventional scalp EEG (19-channel) recordings. Eleven patients with refractory partial seizures, all surgical candidates for whom outcome data is available, underwent preoperative 256 channel EEG recordings. Epileptiform discharges in all cases were recorded. Localization of the spike components of discharges was accomplished by source analysis techniques. These findings were then visualized on standard MRI models. Results obtained using all 256 channels in the analysis were compared to results obtained by subsampling the dense-array data to simulate the information that would be gained from conventional EEG. When compared to standard EEG recordings, increasing the spatial sampling of scalp EEG up to 256 channels improved the detection of discharges, reduced the margin of error in source analysis calculations, and enhanced the reliability of spike localization. The noninvasive spatial resolution of epileptiform discharges may be greatly improved by dense array scalp EEG recordings. This enhanced capability may have implications in studies that examine the utility of dense-array EEG studies in predicting interictal activity recorded by intracranial electrodes, the extension of dense-array recording to 24-hour monitoring, and the accuracy of both interictal and ictal dense array EEG in localization of the seizure onset zone in relation to surgical outcome