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Endogenous circadian rhythms in neurobehavioral functions, including physiological
alertness and cognitive performance, have been demonstrated using special laboratory
protocols that reveal the interaction of the biological clock with the sleep homeostatic
drive. Individual differences in circadian rhythms and genetic and other components
underlying such differences also influence waking neurobehavioral functions. Both
acute total sleep deprivation and chronic sleep restriction increase homeostatic sleep
drive and degrade waking neurobehavioral functions as reflected in sleepiness, atten-
tion, cognitive speed, and memory. Recent evidence indicating a high degree of stabil-
ity in neurobehavioral responses to sleep loss suggests that these trait-like individual
differences are phenotypic and likely involve genetic components, including circadian
genes. Recent experiments have revealed both sleep homeostatic and circadian effects
on brain metabolism and neural activation. Investigation of the neural and genetic
mechanisms underlying the dynamically complex interaction between sleep homeo-
stasis and circadian systems is beginning. A key goal of this work is to identify bio-
markers that accurately predict human performance in situations in which the
circadian and sleep homeostatic systems are perturbed.
1. INTRODUCTION
Sleep is a ubiquitous biological imperative that appears to be evolu-
and intensity (depth) without circadian disruption is necessary to promote
high levels of attention and cognitive performance during the wake period,
and to prevent physiological changes that may predispose individuals to
the past decade. These negative cognitive and health consequences of sleep
restriction are provocative, given that current representative surveys indicate
35-40% of the adult US population report sleeping less than 7 h on weekday
deficits in behavioral alertness and vigilant attention.
10
A lifestyle of chronic partial sleep loss that is often paired with chronic
that humans frequently alter the timing and duration of sleep in exchange
for other activities. This altered behavior appears to be prevalent in current
industrialized societies, where the biological imperative to sleep adequately
may be perceived as a flexible commodity that is traded for other activities
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