EXTRACRANIAL LOCALIZATION OF INTRACRANIAL INTERICTAL EPILEPTIFORM ACTIVITY USING LORETA (LOW-RESOLUTION ELECTROMAGNETIC TOMOGRAPHY)

Besides the standard clinical methods of EEG waveshape analysis, mathe matical models for reconstruction of dipolar sources from the digitize d surface EEG have been introduced in epilepsy research. Although usef ul for localizing focal sources, these methods are inadequate for anal yzing widespread epileptiform activity, A recently introduced alternat ive method called LORETA (low resolution electromagnetic tomography, P ascual-Marqui et al., 1994), directly computes the current distributio n throughout the full brain volume, assuming that neighboring, neurona l populations are simultaneously and synchronously activated. In mathe matical terms the method selects the smoothest of all possible 3-dimen sional current distributions, inherently introducing a certain amount of dispersion. In 7 patients. undergoing simultaneous EEG recording fr om 10 intracranial (subdural) and 22 extracranial electrodes, 111 subd ural discharges (61 subtemporal and 50 lateral temporal) were identifi ed. The exact time point of maximal intracranial activity was automati cally identified, and the LORETA solution at that timepoint was comput ed from the surface EEG. Statistical comparison revealed significantly higher LORETA current density in the area corresponding to the subdur ally recorded spike compared to other areas, and a more anterior a;ld more medial LORETA location for subtemporal compared to lateral tempor al spikes. This study indicates that the LORETA technique may become a useful method to localize electrical activity in the brain. (C) 1997 Elsevier Science Ireland Ltd.