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Sleep deprivation is the condition of not having enough sleep; it can be either chronic or acute. A chronic sleep-restricted state can cause fatigue, daytime sleepiness, clumsiness and weight loss or weight gain. It adversely affects the brain and cognitive function. Few studies have compared the effects of acute total sleep deprivation and chronic partial sleep restriction. Complete absence of sleep over long periods is impossible for humans to achieve (unless they suffer from fatal familial insomnia); brief microsleeps cannot be avoided. Long-term total sleep deprivation has caused death in lab animals.
Effects on the brain
Sleep deprivation can adversely affect the brain and cognitive function. A 2000 study, by the UCSD School of Medicine and the Veterans Affairs Healthcare System in San Diego, used functional magnetic resonance imaging (fMRI) technology to monitor activity in the brains of sleep-deprived subjects performing simple verbal learning tasks. The study showed that regions of the brain`s prefrontal cortex displayed more activity in sleepier subjects. Depending on the task at hand, the brain would sometimes attempt to compensate for the adverse effects caused by sleep deprivation.
The temporal lobe, which is a brain region involved in language processing, was activated during verbal learning in rested subjects but not in sleep-deprived subjects. The parietal lobe, not activated in rested subjects during the verbal exercise, was more active when the subjects were deprived of sleep. Although memory performance was less efficient with sleep deprivation, greater activity in the parietal region was associated with better short term memory.
A 2001 study at Chicago Medical Institute suggested that sleep deprivation may be linked to serious diseases, such as heart disease and mental illnesses including psychosis and bipolar disorder. The link between sleep deprivation and psychosis was further documented in 2007 through a study at Harvard Medical School and the University of California at Berkeley. The study revealed, using MRI scans, that sleep deprivation causes the brain to become incapable of putting an emotional event into the proper perspective and incapable of making a controlled, suitable response to the event. Sleep deprivation may have been the underlying cause of the overdose deaths of celebrities Heath Ledger, and Anna Nicole Smith.
A study tested 17 right-handed civilian males, between the ages of 2129 years (mean 24.7 ± 2.8 years), with no history of medical, neurological, psychiatric, or sleep disorder conditions. Their histories also included 78 h of nightly sleep on a regular basis, no nicotine use, and low caffeine use (less than 100 mg/day). The negative effects of sleep deprivation on alertness and cognitive performance suggest decreases in brain activity and function, primarily in the thalamus, structure involved in alertness and attention, and in the prefrontal cortex, a region sub-serving alertness, attention, and higher-order cognitive processes.
This study used a combination of positron emission tomography (PET) and Fluorine-2-deoxyglucose (FDG), a marker for regional cerebral metabolic rate for glucose (CMRglu) and neuronal synaptic activity. A time series design was used, with progressive sleep deprivation as the independent variable. Repeated measures of absolute regional CMRglu, cognitive performance, alertness, mood, and subjective experiences were collected after 0, 24, 48, and 72 h of sleep deprivation. Additional measures of alertness, cognitive performance, and mood were collected at fixed intervals throughout the sleep deprivation period. These measures were included to place the performance results associated with the PET scans in the context of the circadian rhythm of cognitive performance, as well as to impose a moderate-to-heavy near continuous workload on the subjects as might be anticipated in a real-world sustained operation.
A noted 2002 University of California animal study indicated that non-rapid eye movement sleep (NREM) is necessary for turning off neurotransmitters and allowing their receptors to "rest" and regain sensitivity which allows monoamines (norepinephrine, serotonin and histamine) to be effective at naturally produced levels. This leads to improved regulation of mood and increased learning ability. The study also found that rapid eye movement sleep (REM) deprivation may alleviate clinical depression because it mimics selective serotonin reuptake inhibitors (SSRIs). This is because the natural decrease in monoamines during REM is not allowed to occur, which causes the concentration of neurotransmitters in the brain, that are depleted in clinically depressed persons, to increase. Sleep outside of the REM phase may allow enzymes to repair brain cell damage caused by free radicals. High metabolic activity while awake damages the enzymes themselves preventing efficient repair. This study observed the first evidence of brain damage in rats as a direct result of sleep deprivation.
Animal studies suggest that sleep deprivation increases stress hormones, which may reduce new cell production in adult brains.[