Experimental sectionTest-retest reliability of spectral parameters of the EEG☆
Abstract
The topic of this paper is the intraindividual stability of the EEG at rest for repeated recordings with respect to two sets of spectral parameters. Variability arises due to changes in experimental conditions (such as vigilance) and also due to the inherent random elements of the EEG. The two sets of parameters considered are broad-band parameters and parameters characterizing rhythmic and ‘diffuse’ activity separately, derived from autoregressive fitting. In spite of some imprecision in the definition of the EEG at rest, satisfactory test-retest correlations were found. They proved to be quite homogeneous topographically, but not across frequency bands: delta power is less reliable and to some extent also beta activity, whereas the alpha bands perform well.
The frequency of the alpha rhythm shows a good reliability and, given the difficulties involved with the concept, also the degree of synchronization. The power of rhythmic and of diffuse activity showed more modest retest correlations, probably to be attributed to methodological problems in determining these quantities. On the whole, the results confirm that the normal EEG can be treated as an intraindividually rather stable trait, that artifacts play a minor role in this respect and that 20 sec of activity are sufficient to reduce adequately the variability inherent in the EEG.
Résumé
Le sujet de cet article est la stabilité intra-individuelle de l'EEG de repos lors d'enregistrements répétés, ceci à partir de deux ensembles de paramètres spectraux. L'augmentation de la variabilité est due à des modifications des conditions expérimentales (telles la vigilance) ainsi qu'aux éléments aléatoires inhérents à l'EEG. Les deux ensembles types de paramétres considérés sont les paramètres de bande large et ceux individualisant une activité rythmique et diffuse à partir d'une évaluation autorégressive. En dépit de quelques imprécisions dans la définition de l'EEG de repos, des corrélations entre tests renouvelés satisfaisantes ont été trouvées. Elles se sont montrées tout à fait homogènes topographiquement, mais non entre bandes de fréquences: la puissance delta est moins fiable et dans une certaine mesure, l'activité bêta, alors que pour la bande alpha les résultats sont bons.
La fréquence du rythme alpha présente une bonne fiabilité ainsi que son degré de synchronisation compte tenu des difficultés mêmes qu'offre cette notion. La puissance de l'activité rythmique et diffuse a apporté des corrélations plus modestes entre tests, probablement à cause de problèmes méthodologiques de détermination de ces quantités. En somme, ces résultats confirment le fait que l'EEG normal peut être traité comme une caractéristique intra-individuelle plutôt stable, que les artéfacts ne jouent à cet égard qu'un rôle mineur et que 20 sec d'activité sont suffisantes pour réduire de façon acceptable la variabilité inhérente à l'EEG.
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This work has been performed as part of the research program of the Sonderforschungsbereich 116 (Project M2) and the Sonderforschungsbereich 123 (Project B1), both at the University of Heidelberg, and was made possible by financial support from the Deutsche Forschungsgemeinschaft.