HOW REPRODUCIBLE IS THE TOPOGRAPHICAL DISTRIBUTION OF EEG AMPLITUDE

If topographical EEG is to be a useful tool for localising cerebral pr ocesses, then the results of the same, or closely similar experiments, using different samples should yield similar results. Although the re liability of EEG is well established in other ways, there is little av ailable data on the reproducibility of EEG topography across experimen ts. The aim of this study was to determine the reproducibility of topo graphical EEG by comparing the results of two independently conducted experiments. EEG was recorded during an Eyes Open baseline and a motor task condition (the Luria finger opposition task) in two independent samples of healthy subjects. EEG was recorded in 2.56-s epochs and ana lysed by FFT into conventional theta, alpha and beta, frequency bands. The EEG amplitude for each subject in each frequency range was averag ed over a minimum of 60 s. Separate group averages for each sample wer e calculated and the resulting topographical distributions of electric al potential and current density were compared. The results indicated that the reproducibility of electrical potential in the theta and beta , frequency ranges was extremely poor and only approached acceptable l evels in alpha. Reproducibility of current source density was poor in all frequency ranges. Although some improvement in reproducibility was obtained following spatial smoothing for alpha potential, the highest reproducibility achieved was only 0.65. Reasons for the poor reproduc ibility of topographical EEG and the implications of these findings ar e discussed. (C) 1997 Elsevier Science B.V.