Interindividual variability of lithium-induced EEG changes in healthy volunteers

A placebo-controlled, double-blind study on the effects of lithium on the electroencephalogram (EEG) was performed in 20 healthy volunteers. A reanalysis of the data which previously had been evaluated by factor analysis and other techniques is presented. The aim of this reanalysis is a quantitative reconstruction of visually defined vigilance stages. In 8 of the 10 healthy subjects who received lithium, a "stabilization" of vigilance on a slightly lowered level (i.e., increased continuity of alpha activity and a tendency in the direction of increased alpha anteriorization) could be demonstrated after a 2-week medication period (mean lithium plasma level: 0.65 mmol/l), indicating that in these subjects lithium counteracts the physiological decline of vigilance to be expected under resting conditions. The interpretation of this finding as a reduction of physiological variability, or as a "dynamic restriction," corresponds to findings in other areas of lithium research which can be interpreted in an analogous manner. In two subjects, however, a small decline of vigilance was observed. These two subjects showed an especially pronounced alpha rhythm in their predrug EEG compared with the other volunteers. The authors discuss whether the delineation of different EEG reaction types contributes to the responder problem in lithium research.