Sleepiness on the job: continuously measured EEG changes in train drivers.

Eleven train drivers participated in the study during 1 night and 1 day journey (4.5 h) over the same route. Their EEG, EOG and ECG were recorded on portable tape recorders. The EEG records were subjected to spectral analysis (FFT) and the EOG was scored visually for slow eye movements (SEMs). The results showed that rated sleepiness increased sharply during the night journey. A similar pattern was seen for spectral power density in the alpha band, SEM and, to a lesser extent, also for power in the theta and delta bands. Heart rate was low during the entire night drive. The day journey showed low values without any trend for all variables. The intra-individual correlations were very high between rated sleepiness and, particularly, alpha and theta power density, as well as SEM. Further analyses showed that most of the night time increases in EEG/EOG parameters were confined to the 6 most sleepy subjects. Among these, 4 admitted to dozing off during the night drive and 2 of these 4 subjects failed to act on signals while exhibiting large bursts of alpha activity. It was concluded that EEG and EOG parameters closely reflect variations in sleepiness on the job and that these parameters, together with self-ratings, demonstrate that severe sleepiness may occur in train drivers during night work.