Cerebral electrical fields during petit mal absences.

The electrical fields of spike-wave complexes were plotted with the aid of a microcomputer in patients suffering from petit mal absences. The maximum positivity as well as negativity of the individual complexes was mainly in the frontal areas. While this observation was quite constant among different patients and different seizures within the same patient, the way in which these maxima were reached varied markedly. Even in the most regular patterns, successive spike-wave complexes within one seizure could show different origins and different spread of the field. Positive and negative components of the wave and occasionally of the spike could show different areas of onset. The earliest positive change was frequently in one occipital area or at Pz while negativity could be initiated in frontal or posterior head regions. The variability of onset and spread tended to be somewhat more marked for the positive rather than negative component. The spread of the field over the scalp was at times somewhat discontinuous and one or more preliminary peaks could occur which either disappeared or coalesced before the maximum was reached. The findings suggest that several intracortical generators contribute to the formation of the spike-wave complex but the frontal areas play the most crucial role and medial as well as lateral portions appear to be involved.