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**Sleep deprivation**

Sleep deprivation can have serious effects on your health in the form of physical and mental impairments. Inadequate rest impairs our ability to think, handle stress, maintain a healthy immune system and moderate our emotions. In fact, sleep is so important to our overall health that total sleep deprivation has been proven to be fatal: lab rats denied the chance to rest die within two to three weeks.

Similarly, the brain's ability to problem solve is greatly impaired. Decision-making abilities are compromised, and the brain falls into rigid thought patterns that make it difficult to generate new problem-solving ideas. Insufficient rest can also cause people to have hallucinations. Other typical effects of sleep deprivation include:
 * depression
 * heart disease
 * hypertension
 * irritability
 * slower reaction times
 * slurred speech
 * tremors.

Complete absence of sleep over long periods is impossible to achieve; brief microsleeps cannot be avoided. Sleep deprivation can adversely affect brain function. A 2000 study, by the UCSD School of Medicine and the Veterans Affairs Healthcare System in San Diego, used also functional magnetic resonance imaging 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 lack of sleep. 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 memory. A 2001 study at Chicago Medical Institute suggested that sleep deprivation may be linked to more serious diseases, such as heart disease and mental illnesses including psychosis and bipolar disorder. The link between sleep deprivation and psychosis (psychiatric disorders) 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 lack of sleep 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. A 2002 University of California animal study indicated that REM sleep was 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 REM sleep deprivation may alleviate clinical depression because it mimics [|selective serotonin reuptake inhibitors] (SSRI). 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.
 * Sleep deprivation**, a sleep disorder characterized by having too little sleep, can be either chronic or acute. Long-term sleep deprivation causes certain death in severe cases, especially with lab animals. A chronic sleep-restricted state can cause fatigue, daytime sleepiness, clumsiness and weight gains.

Effects on growth
A 1999 study found that sleep deprivation resulted in reduced cortisol secretion the next day, driven by increased subsequent slow-wave sleep. Sleep deprivation was found to enhance activity on the Hypothalamic-pituitary-adrenal axis (which controls reactions to stress and regulates body functions such as digestion, the immune system, mood, sex, or energy usage) while suppressing growth hormones. The results supported previous studies, which observed adrenal insufficiency in idiopathic hypersomnia.

Effects on the healing process
A study conducted in 2005 showed that a group of rats which were deprived of REM sleep for five days had no significant effect on their ability to heal wounds, compared to a group of rats not deprived of "dream" sleep. The rats were allowed deep (NREM) sleep. However, another study conducted by Gumustekin et al. in 2004 showed sleep deprivation hindering the healing of burns on rats.

Attention
Among the numerous physical consequences of sleep deprivation, attention deficits are perhaps the most important; attentional lapses in mundane routines can lead to unfortunate results, from forgetting ingredients while cooking to missing a sentence while taking notes. The attentional lapses also extend into more critical domains in which the consequences can be literally life-or-death; traffic accidents and industrial disasters can result from inattentiveness attributable to sleep deprivation. To empirically measure the magnitude of these attention deficits, researchers typically employ the psychomotor vigilance task (PVT) which requires the subject to press a button in response to a light at pseudo-random intervals. Failure to press the button in response to the stimulus (light) is recorded as an error, attributable to the microsleeps that occur as a product of sleep deprivation. Crucially, individuals' subjective evaluations of their fatigue often do not predict actual performance on the PVT. While totally sleep-deprived individuals are usually aware of the degree of their impairment, lapses from chronic (lesser) sleep deprivation can build up over time so that they are equal in number and severity to the lapses occurring from total (acute) sleep deprivation. Chronically sleep-deprived people, however, continue to rate themselves considerably less impaired than totally sleep-deprived participants. Since people usually evaluate their capability on tasks like driving subjectively, their evaluations may lead them to the false conclusion that they are able to perform tasks that require constant attention when their abilities are in fact impaired.

Impairment of ability
The dangers of sleep deprivation are nowhere more apparent than on the road; the American Academy of Sleep Medicine reports that one in every five serious motor vehicle injuries is related to driver fatigue, with 80,000 drivers falling asleep behind the wheel every day and 250,000 accidents every year related to sleep, though the National Highway Traffic Safety Administration suggests the figure for traffic accidents may be closer to 100,000.[ The AASM recommends pulling off the road and taking a 15- or 20-minute nap if you begin to feel drowsy.[ According to a 2000 study published in the British Medical Journal, researchers in Australia and New Zealand reported that sleep deprivation can have some of the same hazardous effects as being drunk. People who drove after being awake for 17–19 hours performed worse than those with a blood alcohol level of .05 percent, which is the legal limit for drunk driving in most western European countries. Another study suggested that performance begins to degrade after 16 hours awake, and 21 hours awake was equivalent to a blood alcohol content of .08 percent, which is the blood alcohol limit for drunk driving in Canada, the U.S., and the U.K. In addition, as a result of continuous muscular activity without proper rest time, effects such as cramping are much more frequent in sleep-deprived individuals. Extreme cases of sleep deprivation have been reported to be associated with hernias, muscle fascia tears, and other such problems commonly associated with physical overexertion. Beyond impaired motor skills, people who get too little sleep may have higher levels of stress, anxiety and depression, and may take unnecessary risks. A new study has shown that while total sleep deprivation for one night caused many errors, the errors were not significant until after the second night of total sleep deprivation. However, combining alcohol with acute sleep deprivation results in a trebled rate of driving off the road when using a simulator The National Sleep Foundation identifies several warning signs that a driver is dangerously fatigued, including rolling down the window, turning up the radio, trouble keeping your eyes open, head-nodding, drifting out of your lane, and daydreaming. If you notice one of these cautionary signals, you should pull off the road and take a nap, even if you do not feel especially tired. At particular risk are lone drivers between midnight and 6AM, when the circadian rhythm is at its lowest point Sleep deprivation can negatively impact performance in professional fields as well, potentially jeopardizing lives. Due largely to the February crash of a regional jet in Buffalo, N.Y., which killed 50 people and was partially attributed to pilot fatigue, the FAA is reviewing its procedures to ensure pilots are sufficiently rested. A 2004 study also found medical residents with less than four hours of sleep a night made more than twice as many errors as residents who slept for more than seven hours a night, an especially alarming trend given that less than 11% of surveyed residents were sleeping more than seven hours a night.

Microsleeps
Microsleeps occur when a person has a significant sleep deprivation. The brain automatically shuts down, falling into a sleep state for a period that can last 10 to 60 seconds. The person mentally falls asleep no matter what activity he or she is engaged in. Microsleeps are similar to blackouts and a person experiencing them is not consciously aware that they are occurring. Great sleep deprivation mimics psychosis: distorted perceptions can lead to inappropriate emotional and behavioral responses.

Obesity
Several large studies using nationally representative samples suggest that the obesity problem in the United States might have as one of its causes a corresponding decrease in the average number of hours that people are sleeping. The findings suggest that this might be happening because sleep deprivation could be disrupting hormones that regulate glucose metabolism and appetite. The association between sleep deprivation and obesity appears to be strongest in young and middle-age adults. Other scientists hold that the physical discomfort of obesity and related problems, such as sleep apnea, reduce an individual's chances of getting a good night's sleep.