Electroencephalography and subjective ratings of sleep deprivation

BACKGROUND AND PURPOSE: Sleep-related vehicle accidents account for many injuries and fatalities each year on monotonous motorways and roads. To effectively prevent such incidents requires greater knowledge of the mechanisms and development of the effects of sleep deprivation. Ten volunteers participated in a laboratory study aimed to analyze the way changes in wakefulness were described in terms of EEG changes and subjective ratings. PATIENTS AND METHODS: For each subject, the study consisted of four testing sessions that varied in length on different days: one session each of 60, 90, and 120 min when sleep-deprived, and one session of 120 min when rested. Changes in wakefulness were analyzed using electroencephalographic recordings and ratings on two different scales, the Karolinska Sleepiness Scale (KSS) and the Category-Ratio Scale (CR-10). RESULTS: The results indicate quite conclusively that significant changes in the perception of sleepiness occur during the first 60-90 min of sedentary, monotonous work. Beyond this time period, subjective and physiological changes remained constant throughout the rest of the 120-min period. CONCLUSION: In general, the subjective rating scales highly and significantly correlated with theta activity in both tired and rested states and with alpha activity in the rested state. Similar results were seen using both subjective rating scales.