Daytime sleepiness in insomnia: behavioral, biological and subjective indices.

We compared three measures of daytime sleepiness, sleep behavior (as measured by the multiple sleep latency test), a biological index of sleepiness (pupillometry) and subjective sleepiness (as measured by the Stanford Sleepiness Scale), in evaluating middle-aged individuals with psychophysiological insomnia (n = 20) or no sleep problem (n = 20). Subjects underwent polysomnography (PSG) and four multiple sleep latency test/pupillometry trials the following day. The results determined that neither behavioral, biological nor subjective indices distinguished these two groups. Differentiating the insomniacs into true insomniac (n = 14) and normal sleeping insomniac (insomniacs with sleep efficiency greater than 90%, n = 6) subgroups based upon PSG did not improve daytime discriminations. Furthermore, nighttime sleep experience, measured by either PSG or self-report, was not a strong predictor of these daytime indices among either insomniacs or noninsomniacs. The results of this study support the conclusions that insomniacs do not exhibit heightened levels of daytime sleepiness and that routine fluctuations in sleep exert minimal influence on daytime sleepiness among insomniacs and noninsomniacs. The former finding is likely due either to insomniacs satisfying their biological sleep need despite poor sleep or chronic physiological hyperarousal preventing both sleep and sleepiness.