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When I don't get enough sleep, (a scenario that has become more frequent with my entrance into college), I feel physically sick. I lose my appetite, I get headaches, I can't concentrate, I get cranky, clumsy, and in a generally bad mood. "Hmmm. . . my body must be telling me something," I thought to myself, "sleep deprivation must not be very healthy." I decided to take this opportunity to find out what short-term effects and long term effects sleep deprivation has on people. Could it be that I actually damage my body by not getting enough sleep?
"Sleep is a natural state of rest characterized by reduced body movement and decreased awareness of surroundings" (1). The study of sleep has been greatly enhanced over the last 20 years by the development of sleep-monitoring machines called electroencephalographics (EEG's). EEG's allow scientists to monitor levels of brain activity during sleep (1). There are two general types of sleep; rapid-eye-movement (REM) sleep, and non-rapid-eye-movement (NREM) sleep. Brain waves during REM sleep are more similar to those of wakefulness (1). Scientists believe that dreams occur within the REM state. Adults spend on average 20 percent of their sleeping time in REM sleep (1). NREM sleeping is characterized by much slower brain wave activity.
Although all humans, mammals and birds sleep, scientists do not know precisely why. One theory is that sleep evolved in order to protect animals from predators during the most dangerous times of the day by reducing their action for a long period of time (1). Sleep most likely serves some biological functions because humans and other animals react in the same ways to sleep loss.
So we all need sleep. What happens when we don't get enough? In exploring this question, scientists have produced a wealth of information and theories. I looked at some studies done on the effects of sleep loss on cognition, the ability to function, memory consolidation, and even on the body's endocrine cycle and aging. The scientific community generally accepts some of these studies while some remain very controversial.
Many studies have been performed on the effects of REM sleep deprivation on cognitive tasks. In one such study, presented in the Sleep and Cognitive Function by Allan Hobson (2), a simple visual task called the "visual discrimination task" was given to 26 subjects. Half of the subjects performed the task immediately before going to sleep and then again in the morning, while the other half performed the task only in the morning (2). Performance in the morning was significantly better than in the evening and the improvement of the individual subjects correlated with the amount of REM sleep they had during the night. Interestingly, this correlation did not hold true for all portions of the night (2).
"When the improvement of individual subjects was plotted against the amount of REM sleep during each of the first three quarters of the night, no correlations were observed. . .in contrast, when the improvement of individual subjects was plotted against the amount of REM sleep during the final quarter of the intervening night, the correlation was highly significant" stated Hobson(2). "Hmm. . ," I thought to myself, "if the learning takes place during the final quarter of the night, that means that getting up early in the morning could be more harmful than staying up late at night. Could it be actually good for me to sleep in?" Probably not; the study showed that a different type of sleep altogether, called Slow Wave Sleep (SWS), is also when a lot of the learning takes place. SWS occurs in the first quarter of sleep (2). "POP!!" (the sound of Robin's bubble popping-I can't justify staying up late and sleeping in).
The second part of the study was not about how sleep affects cognition, but rather the exact opposite. Hobson went on to show that the amount of cognition that takes place before sleep effects the amount and intensity of REM sleep. "Using the same visual discrimination task as in the preceding study, we have shown that task training increases REM sleep on the following night" (2). In conclusion, sleep effects cognition and cognition effects sleep(2).
Since learning and sleeping are so interdependent, not only does cognition suffer from a lack of sleep, but research shows that a person's ability to function in everyday tasks decreases parallel to sleep deprivation. A study has found that insomniacs report memory difficulties, poor performance at work, problems concentrating, and have twice as many fatigue-related car accidents as good sleepers (3). Although these may not surprise many individuals and may seem obvious to others, scientists are still quite skeptical. James K. Walsh of the International Conference of Sleep and Cognitive Function (3). asserts that there are a number of studies showing no difference between insomniacs and noninsomniacs. He makes the point that the experimentation could be faulty because of the ways in which the insomniacs were recruited (3).
Though the research involving insomniacs and everyday function is controversial, the debate regarding the effects of sleep deprivation on memory consolidation is much more heated. Some studies claim that because REM sleep intensifies or increases after successful learning (in both animals and humans) the deprivation of REM sleep following the end of the task results in memory losses that can be up to 50 percent lower than the original acquisition scores (4). However, according to Robert P Vertes Ph. D of Florida Atlantic University (5), "some studies have reported effects [of sleep deprivation] on memory, at least equal numbers have not. Vertes claims that many studies reporting deficits in memory in accordance with REM deprivation use harsh REM deprivation techniques and or deprive subjects of other phases of sleep as well as REM(5). Vertes cites an anecdote about a man who despite the absence of REM sleep due to a brain injury lives a normal functioning life as a practicing lawyer (5). I don't know how "normal" and "functioning" a lawyer's life can be, but assuming that it was this would suggest that REM sleep might not even be necessary (though most scientists believe that it is).
The study that came closest to answering my original question came out of the University of Chicago's Center for Sleep Research (6). The study showed that young adults with chronic sleep loss showed a reduced capacity for metabolic functions like processing and storing carbohydrates, and regulating hormone secretion (6). "Cutting back from the standard eight down to four hours of sleep each night produced striking changes in glucose tolerance and endocrine function-changes that resembled the effects of advanced age or the early stages of diabetes-after less than one week" (6). The difference between this study and some of the previous ones discussed is the evaluation of the subjects after they had already recovered from sleep loss (6).
The study followed 11 men for 16 nights. The first 3 nights they were given 8 hours to sleep, the next 6 nights they were given 4 hours to sleep, and the following 7 nights they slept for 12 hours. Glucose and hormone levels were monitored every 30 minutes on the sixth day of deprivation and recovery (6). Profound alterations of glucose metabolism resembling type-2 diabetes were observed (6). During the height of their sleep deprivation, the subjects took 40% longer than normal to regulate their blood-sugar levels after a high carbohydrate meal, and their ability to secrete and respond to insulin decreased by about 30% (6). This is an early marker of diabetes. The production and action of other hormones were also effected by sleep deprivation (6). Such observations included the "dampening [of] the secretion of the thyroid stimulating hormone and increasing blood levels of cortisol especially during the afternoon and evening" (6). These symptoms are typical of much older subjects and "are thought to be age-related health problems such as insulin resistance and memory impairment" (6). The fact that these endocrine changes mimic aging suggests that sleep debt may have some serious long-term effects.
If this statement is true, I wonder if the amount of sleep a person gets each night is correlated to the life span of that individual. I was told as a child that most of my growing took place when I slept, and that even adults wake up slightly taller in the morning than when they went to sleep. If, during sleep, the mind absorbs, learns and processes the information that it was flooded with during the day, then could better rest be associated with better achievement?
As insomnia effects processes including cognition, functionality, memory, speech, attention, learning, reasoning, planning, creative thinking, and problem solving (8) in the individual, undoubtedly it has negative effects on the society and economics of a country. According to Damien Leger M.D., Ph. D. (7), "Direct costs of insomnia include outpatient visits, sleep recordings and medications." Although more studies are needed to validate this claim, it is possible that sleep deprivation has direct effects on professional life and the cause of accidents in the workplace (7). One study estimated the loss of productivity due to insomnia in the U.S. in 1988 to be 41.1 billion (7).
American culture is known for being "fast-paced" and "high-stress", conditions that are directly related to sleep. This is common in technologically advanced countries. When I lived in Japan, I was consistently shocked by the little amount of sleep that my host family got. Often they wouldn't sleep until 2:00 or 3:00 am and then proceed to wake up at 7:00 am and put in a full day of work. "Cutting back on sleep is an extremely common response to the time pressures of modern industrial societies. The average night's sleep decreased from about 9 hours in 1910 to about 7.5 hours in 1975, a trend that continues. Millions of shift workers average less than 5 hours [of sleep] per work day" (6).
I have always resented teachers for assigning more homework than can be accomplished within the waking hours of one day. Sleep is so important for adolescents (see "Sleep and the Teenager", (9)) far more important than filling out crosswords and memorizing speeches. "It is important to remember that sleep deprivation does have detrimental effects, which we sometimes forget as we push workers, students and others to perform even when they are functioning with a lack of sleep," stated J. Christian Gillin M.D.(10)
We all know the sound of our parent's voices nagging us to get to bed, or the concerned face of a friend who says, "you look like you need a nap". With the recent findings in sleep research, scientists our giving these arguments strength. Though much of the research has yet to be tested and re-tested enough for the scientific community to accept, the correlations make sense with my original hypothesis and question. Sleep almost certainly effects cognition and functionality, and may even effect memory, endocrine cycles, and aging. Now I can truly argue that my time is better spent sleeping. I think I'll go take a nap.
ZZzzzzzzzzzzzz. . .
1) Center for Sleep Research, Siegel Lab
2) Sleep and Cognitive Function: Research and Clinical Perspectives. Sleep and Cognition, J. Allan Hobson
3); Sleep and Cognitive Function: Research and Clinical Perspectives. Chronic Insomnia, Ability to Function and Quality of Life, James K. Walsh
4); Sleep and Cognitive Function: Research and Clinical Perspectives. Sleep States and Memory Consolidation, by Carlyle Smith,
5); Sleep and Cognitive Function: Research and Clinical Perspectives. Debating the Question of Whether Memories Are Consolidated in REM Sleep, By Robert P. Vertes ,
6); Lack of Sleep Alters Hormones, metabolism, simulates effects of aging ,
7); Sleep and Cognitive Function: Research and Clinical Perspectives. Economics/Direct and Indirect Costs of Insomnia, by Damien Leger and Michel Paillard,
8); Sleep and Cognitive Function: Research and Clinical Perspectives. Straight Thinking: How Sleep Loss Throws You a Curve, by Mark Rosekind and Stephanie Hamilton-Oravetz,
9); Sleep and the Teenager, by Stacie C. Link and Sonia Ancoli-Israel,
10); Brain Activity is Visible Altered Following Sleep Deprivation.,
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