Localization of epileptiform foci by means of MEG measurements.

Systematic studies of the magnetoencephalogram (MEG) in normal and pathological subjects (mainly with focal epilepsies) showed that the MEG may evidence significant brain activities even if they are not identifiable in the electroencephalogram (EEG). They also showed that the MEG has a considerably higher spatial resolution than the EEG. A two-dimensional mapping technique was used to get such a representation of the data that would enable the investigator to draw his conclusions mainly from inspecting the plots. The technique is characterized by an isospectral synchronized power (iso-SSP) mapping of the scalp distribution of specified frequency bands of the MEG power spectrum. In this way the precise projection on the scalp of an epileptiform focus can be determined without applying a strong eliciting stimulus or relying on the analysis of the simultaneously recorded EEG. Our results compare very favourably with the clinical picture of our pathological subjects.