Extreme sleepiness: quantification of EOG and spectral EEG parameters.

Our earlier research has shown considerable increases of and intercorrelations between subjective sleepiness, alpha, theta, and delta power density of the EEG as well as slow rolling eye movements (SEM) during night-time, monotonous work tasks. The purpose of the present methodological study was to establish EEG-EOG criteria for extreme behavioral sleepiness. Medilog tape-recorders were used to record EEG and EOG on 5 males and 5 females during a 45 min visual vigilance test. Performance on the test was also recorded on the tape as well as experimenter-scored dozing off episodes (from TV supervision). The EEG was subjected to computerized spectral analysis in 7.5 s epochs, and the EOG was scored visually for slow eye movements in the same epochs. The epochs immediately preceding a hit, miss and dozing off differed significantly. There was most power density in the alpha, theta and delta bands and most SEM activity before dozing off episodes and least before hits. The power density and the SEM activity were significantly increased one whole minute before dozing off events and missed signals compared to hits. Just prior to the ultimate sleepiness, i.e., the dozing off, the SEM activity and the delta and theta power density were further increased, while alpha power density was at its maximum during the last three epochs before the dozing off. The response patterns of all subjects were rather homogeneous. In conclusion, behavioral sleepiness is systematically reflected in spectral EEG and EOG parameters and the results support attempts to use these variables to indicate sleepiness in active subjects in real life situations.