Topographic mapping of brain electromagnetic signals: a review of current technology.

Topographic mapping of brain electromagnetic signals has become increasingly popular in recent years both as a clinical tool and as an area of research in its own right. The capabilities of existing computerized systems for displaying such maps and for performing localization of current sources in the brain have continued to expand. In this paper we review some of the methodological and technological issues concerning topographic mapping. These include issues of choice of interpolation algorithm, what to map, head geometry, EEG reference location, and scaling. We also discuss characteristics of clinical databases for patient comparison and the usefulness of quantitative EEG (which includes mapping) for the diagnosis of nervous system disorders. Finally, we compare five representative systems in terms of their topographic mapping capabilities. The overall conclusion is that future developments must make use of integrated data from other neuroimaging technologies such as MRI, PET, and SPECT, and determination of the normal limits of topographic parameters must be more carefully examined.