Circadian and wakefulness-sleep modulation of cognition in humans

Abstract

Cognitive and affective processes vary over the course of the 24 h day. Time of day dependent changes in human cognition are modulated by an internal circadian timekeeping system with a near-24 h period. The human circadian timekeeping system interacts with sleep-wakefulness regulatory processes to modulate brain arousal, neurocognitive and affective function. Brain arousal is regulated by ascending brain stem, basal forebrain (BF) and hypothalamic arousal systems and inhibition or disruption of these systems reduces brain arousal, impairs cognition, and promotes sleep. The internal circadian timekeeping system modulates cognition and affective function by projections from the master circadian clock, located in the hypothalamic suprachiasmatic nuclei (SCN), to arousal and sleep systems and via clock gene oscillations in brain tissues. Understanding the basic principles of circadian and wakefulness-sleep physiology can help to recognize how the circadian system modulates human cognition and influences learning, memory and emotion. Developmental changes in sleep and circadian processes and circadian misalignment in circadian rhythm sleep disorders have important implications for learning, memory and emotion. Overall, when wakefulness occurs at appropriate internal biological times, circadian clockwork benefits human cognitive and emotion function throughout the lifespan. Yet, when wakefulness occurs at inappropriate biological times because of environmental pressures (e.g., early school start times, long work hours that include work at night, shift work, jet lag) or because of circadian rhythm sleep disorders, the resulting misalignment between circadian and wakefulness-sleep physiology leads to impaired cognitive performance, learning, emotion, and safety.

Circadian rhythms in cognitive performance: implications for neuropsychological assessment

“…14,15,35 In this individual, the level of cognitive performance is low early in the morning (07:00-10:00), in part due to the fact that circadian rhythms reach their lowest point at dawn and in the first hours of the morning. Also, "sleep inertia" of neuropsychological processes in patients with brain disorders.…”

“…Finally, performance decreases at night (22:00-04:00) and reaches its lowest levels at dawn (04:00-07:00). 15 It is important to keep in mind that this time course has been documented in healthy people, and that it is modulated by chronotype, 67 age, 68 and sleep deprivation.…”

“…[12][13][14] Performance also depends on a homeostatic process that involves a decay in execution with time awake (sleep deprivation), whereas sleep restores performance. 15 Variations in human performance may be the result of circadian rhythms in cognitive processes that are crucial for the execution of all tasks. Rhythms in cognitive performance have been found for three basic neuropsychological processes (attention, working memory, and executive functions), which can modulate the execution of many tasks.…”

The effect of working on-call on stress physiology and sleep: A systematic review

“…We contend that a similar relationship exists between sleep and stress when operating on-call from home ( Figure 1). Other external factors such as wakefulness at inappropriate biological times, may disturb the synchrony of the circadian rhythm and result in impaired cognitive function [50,51]. However, these factors are outside the scope of the review and are not included in the model.…”

Circadian waveform bifurcation, but not phase-shifting, leaves cued fear memory intact

“…In rodents and humans, many cognitive tasks show a circadian peak in performance, including acquisition and retrieval of memories [13,14]. Although in many experimental paradigms it is difficult to dissociate the circadian effects of these two stages of memory, a number of recent studies have elegantly succeeded in doing so.…”