Brain source imaging of focal and multifocal epileptiform EEG activity

Brain electric source analysis (BESA) of the scalp EEG has been used to identify multiple equivalent current sources in the brain during during interictal spikes and seizure onset. To obviate the need for fitting dipole sources to every EEG segment, a new method has been developed on the basis of multiple fixed dipoles, each designed to emphasize functional imaging of particular cortical areas. "FOCUS" can quickly display EEG in various montages including new "sources montages" which provide a high sensitivity for source currents near each dipole while largely suppressing contributions from other brain areas. By comparing this "source EEG" to routine digital EEG in patients with complex partial epilepsy, we have observed that "FOCUS" can more readily determine whether an epileptiform discharge is consistent with a discrete or multifocal generator, characterize likely cerebral source(s), differentiate between spikes and seizures of mesio-basal versus lateral temporal or frontal origin, and estimate the presence and direction of propagation from source potential timing differences. Improved non-invasive EEG evaluations of partial epilepsy will undoubtedly result from this advance.