Calibration of an objective alertness scale

Area of Science:

• Neuroscience
• Psychology
• Sleep Science

Background:

• Objective scales for alertness-sleepiness require calibration against subjective measures, such as the Karolinska Sleepiness Scale (KSS).
• Prolonged wakefulness can introduce disagreements between objective and subjective sleepiness assessments.
• The reliability of subjective reports poses challenges for calibrating objective scales.

Purpose of the Study:

• To evaluate the impact of extended wakefulness on the discrepancy between objective and subjective sleepiness assessments.
• To determine if an objective alertness-sleepiness scale can be reliably calibrated despite limitations in subjective report reliability.

Main Methods:

• Electroencephalogram (EEG) recordings were taken at 2-hour intervals during prolonged wakefulness (44-61 hours) in 15 healthy participants.
• Objective alertness scores were derived from EEG spectral analysis (principal component and alpha-theta power).
• Objective scores were calibrated against subjective Karolinska Sleepiness Scale (KSS) ratings.

Main Results:

• A strong correlation was observed between the time courses of objective and subjective sleepiness scores.
• Systematic errors in both the mean and calibration of the objective scale were identified.
• Error correction significantly strengthened the correlation (r = 0.99) and established a one-to-one correspondence between objective and subjective scales.

Conclusions:

• The calibrated objective alertness scale effectively mirrors subjective sleepiness levels.
• Scores from 5 to 0 on the objective scale correspond to distinct levels of sleepiness: minimal, mild, moderate, marked, severe, and disabling.
• This validated objective scale offers a reliable measure for assessing alertness and sleepiness.