Life Science
Night Terrors
What happens when we sleep, what happens when we don't, and why naps are good.



   

With all of its variables and mysteries, sleep (like the weather) provides for an endless source for small talk. How did you sleep, and did you get enough? Was it hard to fall asleep, or hard to wake up? Did you dream, and what about?

It’s unclear why, but people need sleep to survive. Insects, fish, and animals need it, too, but some less and others more, some hibernating for months. Sometimes sleep eludes people, no matter how tired they are, and other times the well-rested can’t stop themselves from nodding off throughout the day. People dream, but often can’t remember what about, or they dream the same thing over and over and over again.

Sleep is fascinating, and not just to regular people, but also to scientists who can now use technology like fMRI and modern biochemical tools to better understand it. A lot of work has gone into answering one question in particular: What happens when people don’t get enough sleep?

Chronic sleep deprivation is widely considered a side effect of living in a 24/7 society. It’s even documented that people living in industrialized nations get about an hour less sleep a night than they did 40 years ago. But until recently, people generally considered the effects of such sleep to be inconsequential.

If only. A study last summer showed how, contrary to common wisdom, our bodies can’t make up for chronic sleep loss. The authors suggested that the accumulated deficit did more than just make people feel a little tired or short-tempered. Chronic sleep loss of even two to three hours per night held the potential to hamper body and mind functioning, not to mention quality of life.

The list of insidious effects of chronic sleep loss is growing fast, based on a surge of new findings:

- Sleep deprivation impairs memory and thinking. Adequate sleep is necessary in order for procedural skills, like learning to play an instrument or a sport, to become more automatic. It is also necessary for spatial learning, such as learning how to get to a new destination. While learning spatial tasks increases the production of new cells in the hippocampus, those new brain cells cannot survive without adequate sleep.

- Sleep deprivation adversely affects decision-making. The nucleus accumbens — an area in the brain involved with the anticipation of reward — becomes more active during gambling when high risk-high payoff choices are made under conditions of sleep deprivation. The expectation of reward for the high-risk gamble is also elevated. Sleep-deprived people also take longer to respond to moral dilemmas, suggesting that sleep loss makes it harder to decide on the right course of action.

- Sleep deprivation boosts the part of the brain most closely connected to depression, anxiety, and other psychiatric disorders. Without sleep, the emotional centers of the brain dramatically overreact to negative experiences, leading to emotionally irrational behavior, due to a shutdown of the prefrontal lobe — a region that normally keeps emotions under control.

- Sleep deprivation increases the chances of gaining weight. This may be because partial sleep deprivation alters the circulating levels of the hormones that regulate hunger, increasing appetite and a preference for calorie-dense, high-carbohydrate foods. One study even found that people who slept less were more likely to become obese even though they consumed fewer calories than the people who slept a full night.

- Sleep deprivation diminishes long-term health overall, including adversely affecting endocrine functions and metabolic and inflammatory responses. This suggests that chronic sleep restriction might increase the risk for serious chronic diseases such as high blood pressure, diabetes type II, and heart disease.

In sum, people should be sleeping the recommended 7 to 8 hours per night, but they are actually sleeping significantly less. Perhaps naps are the answer here. Benefits would likely include improvements in overall health and happiness. The body is on a basically 24-hour body clock that winds down once in the afternoon and once in at night. Available research shows that a nap after a big lunch is natural, since the neurons that keep us alert become turned off after we eat. A daytime nap can boost learning and memory by helping us tune-out interfering information, and it can reduce the risk of dying from heart disease by as much as one-third compared to non-nappers.

Sounds like a very good thing, indeed. Is it too late for Americans to adopt the practice of the European siesta? • 31 January 2008

SOURCES: “Repeated sleep restriction in rats leads to homeostatic and allostatic responses during recovery sleep,” Kim Y, Laposky AD, Bergmann BM, & Turek FW. Proc Natl Acad Sci USA. 2007;104:10697-702. “Sleep restriction suppresses neurogenesis induced by hippocampus-dependent learning,” Hairston IS, Little MT, Scanlon MD, et al. J Neurophysiol. 2005;94:4224-33. “Sleep and memory: the ongoing debate,” Stickgold R & Walker MP. Sleep. 2005;28:1225-7. “Inadequate sleep as a risk factor for obesity: analyses of the NHANES I,” Gangwisch JE, Malaspina D, Boden-Albala B, Heymsfield SB. Sleep. 2005;28:1289-96. “The effects of 53 hours of sleep deprivation on moral judgment,” Killgore WD, Killgore DB, Day LM, Li C, Kamimori GH, Balkin TJ. Sleep. 2007;30:345-52. “Sleep deprivation elevates expectation of gains and attenuates response to losses following risky decisions,” Venkatraman V, Chuah YM, Huettel SA, & Chee MW. Sleep. 2007;30:603-9. “The human emotional brain without sleep--a prefrontal amygdala disconnect,” Yoo SS, Gujar N, Hu P, et al. Curr Biol. 2007;17:R877-8. “Behavioral and physiological consequences of sleep restriction,” Banks S & Dinges DF. J Clin Sleep Med. 2007;3:519-28. “Tandem-pore K+ channels mediate inhibition of orexin neurons by glucose,” Burdakov D, Jensen LT, Alexopoulos H, et al. Neuron. 2006;50:711-22. “Siesta in healthy adults and coronary mortality in the general population,” Naska A, Oikonomou E, Trichopoulou A, et al. Arch Intern Med. 2007;167:296-301. “Daytime sleep condenses the time course of motor memory consolidation,” Korman M, Doyon J, Doljansky J, et al. Nat Neurosci, 2007;10:1206-1213.



Jennifer Fisher Wilson is the science reporter for Annals of Internal Medicine. Her stories are available at www.annals.org. Life Science appears here every other week.





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The World's Most Famous Napper
"Don’t think you will be doing less work because you sleep during the day. That’s a foolish notion held by people who have no imagination."
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