Methods to improve spatial resolution of EEG

Given the complexity of neocortical source activity which largely determines observed EEG phenomena, it is of interest to categorize four types of sources. Whereas dipole localization methods are generally applicable only to one of these types, methods to improve spatial resolution apply to all four types of sources. The four types are: type I, localized and stationary, i.e., EEG due to a single dipole source that remains at fixed location over some time scale of interest in a particular application; type II, distributed and stationary, i.e., EEG sources form a dipole layer but important spatial characteristics remain relatively constant over the period of interest; type III, localized and nonstationary, i.e., EEG due to dipole source which move between a small number of well-defined locations; and type IV, distributed and nonstationary. Most EEG phenomena probably fit this last category, depending on accuracy required and length of time scale.<>