Introduction
Focal epileptic lesions in certain regions of the brain may produce bilaterally synchronous electroencephalographic (EEG) abnormalities that simulate more or less closely the wave-and-spike pattern of true petit mal (Tükel and Jasper, 1952; Bates, Cobb, and Williams, 1956; Ajmone-Marsan and Ralston, 1957). Jasper has termed the latter "primary bilateral synchrony" and the former "secondary bilateral synchrony," on the presumption that epileptiform discharges arising in these cortical regions (medial or orbital surface of the frontal lobe, or, less frequently, the medial surface of the temporal lobe), spread via corticofugal pathways into subcortical gray matter localized in the upper midbrain and diencephalon, the hypothetical midline centren-cephalic system, with secondary activation of this system (Penfield and Jasper, 1954). According to this view, the result of epileptiform activity of the centrencephalic system, whether primary or secondary, is the same—i.e., bilaterally synchronous waveand-spike complexes appearing simultane ously in both cerebral hemispheres. The EEG