<p>There is a need for empirical indicators that can track subtle changes in wakefulness with high temporal resolution. The aim of the present work was to evaluate the applicability of a number of indexes based on the mean spectral power of EEG rhythms, as well as the BIS index, which is used in anesthesiology. Twenty-six volunteers took part in an experiment involving forced awakening from stage 3 daytime sleep: subjects were required to solve visual-motor and arithmetic problems immediately after the alarm sounded. Artifact-free segments were extracted from EEG recordings at different levels of wakefulness: during sleep, on awakening, at partial wakefulness (when task performance was still difficult), and in full wakefulness (when the ability to solve problems correctly was restored). EEG indexes were calculated for these segments, and the ability of each index to differentiate these states was analyzed. The results revealed that the most indicative indexes were γ/β, β/δ, γ/δ, a Complex index ((α + β)/(δ + θ)), and the BIS index. The dependence of these indexes on muscle and oculomotor artifacts was then assessed, as was the extent to which their values changed on opening or closing the eyes. Muscle artifacts had the greatest impact on the γ/β index, while eye movement artifacts had the greatest impact on the β/δ, γ/δ, and Complex indexes. Artifact removal by filtration and ICA significantly improved their indexes. Ultimately, the BIS index proved to be the most informative – it was less dependent on both muscle and oculomotor artifacts. The data here obtained indicate that EEG indexes can provide a convenient tool for tracking subtle changes in the level of wakefulness; however, the accuracy of the results can be increased by using a combination of several different indexes.</p>