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Deficits in cognitive performance due to continuous sleep restriction are not well understood. Studies have looked into physiological arousal of the sleep-deprived brain. Participants, whose total amount of sleep had been restricted by 33% throughout one week, were subjected to reaction time tests.
Sleep deprivation, also known as sleep insufficiency [2] or sleeplessness, is the condition of not having adequate duration and/or quality of sleep to support decent alertness, performance, and health. It can be either chronic or acute and may vary widely in severity.
One of the important questions in sleep research is clearly defining the sleep state. This problem arises because sleep was traditionally defined as a state of consciousness and not as a physiological state, [14] [15] thus there was no clear definition of what minimum set of events constitute sleep and distinguish it from other states of partial or no consciousness.
Sleep increases the sensory threshold. In other words, sleeping persons perceive fewer stimuli, but can generally still respond to loud noises and other salient sensory events. [14] [12] During slow-wave sleep, humans secrete bursts of growth hormone. All sleep, even during the day, is associated with the secretion of prolactin. [15]
Deep sleep refers to slow-wave sleep — a stage in the sleep cycle when brain waves slow down. Getting enough deep sleep is crucial for numerous bodily functions.
During sleep, the hippocampus replays the events of the day for the neocortex. The neocortex then reviews and processes memories, which moves them into long-term memory. When one does not get enough sleep it makes it more difficult to learn as these neural connections are not as strong, resulting in a lower retention rate of memories.
Since the REM stages typically occur during the second half of sleep, sleeping too little may not allow the body enough time to complete all the REM sleep cycles, per the National Sleep Foundation.
Sleep debt or sleep deficit is the cumulative effect of not getting enough sleep. A large sleep debt may lead to mental or physical fatigue, and can adversely affect one's mood, energy, and ability to think clearly. There are two kinds of sleep debt: the result of partial sleep deprivation, and of total sleep deprivation