A critical review of clinical applications of topographic mapping of brain potentials.

A brief review of several aspects of topographic mapping of brain potentials is presented. Some general factors of importance for the construction of brain maps are considered, namely, how to sample in space and how to deal with the influence of the reference electrode. The issue of what is a representative map is examined for the cases of both steady and dynamic states. Special attention is paid to the methodology of assessing whether a brain map may be considered "normal" or "abnormal" on the basis of multivariate statistical considerations. Besides being used to visualize statistical comparisons between sets of EEG data, brain maps may be used as a first step for a model-based analysis in order to estimate the localization of equivalent dipolar sources of the electrical activity within the brain. The question of whether brain maps may yield added value to multivariate quantitative EEG analysis is examined for the following clinical cases: (1) developmental disorders; (2) space-occupying lesions; (3) epilepsy; (4) cerebrovascular diseases; (5) dementia; and (6) psychiatric diseases. It is concluded that brain mapping may be valuable as a comprehensive and attractive form of data reduction to represent a complex set of multichannel (optimally at least 64) EEG signals, but only if the user is well aware of the pitfalls involved. Brain mapping might supplement quantitative topographic analysis if it can be used as the basis for solving the inverse problem in EEG. More extensive and well-controlled studies are necessary in order to establish the clinical value of complementing a routine EEG examination with brain mapping.