In Press, International Journal of Psychophysiology Pupil Staging and EEG Measurement of Sleepiness

The goal of this multi-method, known-groups measurement study was to examine the validity (accuracy) of the pupillometric Alertness Level Test (ALT) as a physiologic measure of sleepiness. The study used a pooled-time series-correlation design with 16 untreated narcolepsy (8F, 8 M), 16 obstructive sleep apnea (OSA) (7 F, 9 M), and 16 healthy control (8 F, 8 M) subjects extensively screened to determine their eligibility. All participants underwent EEG/polysomnography testing using standard Multiple Sleep Latency Test (MSLT) electrode placement concurrent with the 15 min. pupillometric ALT. Data were collected in a quiet dark environment with subjects seated in a comfortable chair with eyes open and staring at a red spot. EEG data were examined to determine if theta power (4-7 Hz) increased during 2-sec. periods of proportional pupil size decreases (pupil Stage 1, 95% or more of maximal pupil size to Stage 4, 65-74% of maximal size). Printed EEG records were visually scored. Self-report sleepiness measures included the Pittsburgh Sleep Quality Index (PSQI), the Profile of Mood States (POMS), and the Epworth Sleepiness Scale (ESS). Within subject groups, theta power ratios significantly increased across pupil stages for the sleep disorder groups but not for controls (theta activity increased 42% for narcoleptic and 36% for OSA subjects). Between subject groups, the amount of theta activity was significantly greater for narcoleptic and OSA subjects than for controls. Visual EEG scoring and self-report measures were usually consistent with objective findings. The ALT is convenient, easily repeatable, and less technically demanding than EEG sleepiness measures, and it deserves more comprehensive testing as a valid measure of sleepiness.