“Reducing sleep time in healthy adults (ages 21-45 years) to between 4 and 6 hours per night results in cumulative increases in daytime cognitive performance deficits that can become quite severe, without the person feeling extremely sleepy.”

The paper reports the findings of the most extensive laboratory-controlled dose-response experiment conducted to date on the effects of chronic sleep restriction on neurobehavioral functions in healthy adults. There has been controversy as to whether or not sleepiness and cognitive effects accumulate when sleep is reduced in duration. Our findings document that cumulative cognitive impairments develop when nocturnal sleep time is reduced below eight hours’ time in bed, and these deficits ultimately reach levels comparable to the deficits found under conditions of acute total sleep deprivation. These findings leave no doubt that this occurs and it is a dose-dependent response (both within and between subjects). The findings fail to support leading sleep theories including the theory of "core" sleep being five to six hours; the theory that slow wave sleep reflects sleep homeostasis; the theory that adaption occurs to sleep loss; and the theory that sleep debt is the primary causative factor in cumulative waking neurocognitive deficits. The paper suggests that the cost of additional wakefulness beyond approximately 16 hours may be the basis for the adverse effects of chronic sleep restriction, and it challenges us to determine what the neurobiological mechanisms may be for cumulative effects on brain functions over many days of sleep restriction.

The paper reports discovery of dose-response near-linear increases in cognitive performance deficits involving attention, working memory and cognitive throughput, across 14 days of sleep restriction. Changes were much less dramatic in subjective ratings of sleepiness and fatigue. The paper is of interest to scientists, clinicians, and policy makers concerned with sleepiness and stable waking neurocognitive functions, relative to sleep need.

Reducing sleep time in healthy adults (ages 21-45 years) to between four and six hours per night results in cumulative increases in daytime cognitive performance deficits that can become quite severe, without the person feeling extremely sleepy. This suggests that the brain has a neurocognitive vulnerability to chronically reduced sleep that is not fully evident in either subjective sleepiness or the physiological makeup of sleep.

I became interested in the effects of sleep loss while in graduate school and spent my scientific career attempting to understand the relationship of sleep to waking neurobehavioral and physiological functions. Much of this time has been devoted to study of the effects of acute sleep loss. With support from the National Institutes of Health, the National Institute of Nursing Research, and the Air Force Office of Scientific Research, and increased improvements in ambulatory electrophysiological monitoring, we were able to complete labor-intensive experiments on chronic sleep restriction in which healthy adults (average age 29 years) spent a grand total of 870 days living in the laboratory, while randomized to various nocturnal sleep dosages. This required specialized facilities to accommodate continuous physiological, behavioral, and cognitive monitoring of volunteers. However, it allowed for a marked advance in scientific control over earlier studies that lacked adequate controls, sample sizes, and measurements. The results were well worth the effort. The experiment provided critical new theoretical and applied evidence regarding sleep need and the consequences of failing to obtain adequate sleep.