The electroencephalogram through a software microscope: non-invasive localization and visualization of epileptic seizure activity from inside the brain

Objective: We developed a novel non-invasive analysis to localize the sourc e and visualize the time course of electrical activity generated inside the brain but unclear from the scalp. This analysis applies to signals with un ique waveform characteristics, such as seizures. Methods: The method extracts activity from an EEG data matrix as a spatiote mporal component having waveforms uncorrelated to the other concurrent acti vities. The method also provides the location and orientation of the dipole generating this activity. We applied this method to ten scalp seizures in three patients with temporal lobe epilepsy and single-focus seizures confir med by intracerebral recordings. A realistic head model based on MRI was us ed for computation of field distributions. Results: When seizure activity was still not visually identifiable on the s calp, the method demonstrated in all scalp seizures a source in the tempora l neocortex corresponding clearly to the region of seizure activity in intr acerebral recordings. Frequency characteristics of the estimated activities also resembled those of the intracerebral seizures. Conclusions: This method enables estimation of focal brain activity when it s effect on scalp EEG is unclear to visual examination. It works in situati ons where currently available source analyses methods, which require noisel ess definite activity, are not applicable. (C) 2000 Elsevier Science Irelan d Ltd. All rights reserved.