Chapter 39 - Circadian Rhythms in Sleepiness, Alertness, and Performance

Abstract

The biologic clock drives circadian rhythms and regulates changes in behavior over the 24 hours of the day. There are circadian rhythms in almost all variables describing alertness and performance. People tend to be less alert in the early morning and late at night, but it also depends on the circumstances. A variety of factors (e.g., activity, posture, light exposure) can mask circadian rhythms. Even with masking influences experimentally controlled, measurements of the endogenous circadian rhythmicity in alertness and performance still reflect the interaction of the biologic clock with the homeostatic regulation of sleep. It has been argued that certain masking factors (e.g., sensory stimulation, body movement) are an integral part of the mechanisms regulating waking neurobehavioral functions. Accounting for their interactions with the biologic clock helps to explain or predict the occurrence of cognitive performance deficits across the circadian cycle.