National Geographic

of those people who are proud of being able tofall asleep quickly just about anywhere, you canstop gloating—it’s a distinct sign, especially ifyou’re less than 40 years old, that you’re acutelysleep deprived.The first segment of the brain that begins tofizzle when we don’t get enough sleep is the pre-frontal cortex, the cradle of decision-making andproblem-solving. Underslept people are moreirritable, moody, and irrational. “Every cognitivefunction to some extent seems to be afected bysleep loss,” says Chiara Cirelli, a neuroscientistat the Wisconsin Institute for Sleep and Con-sciousness. Sleep-deprived suspects held by thepolice, it’s been shown, will confess to anythingin exchange for rest.Anyone who regularly sleeps less than sixhours a night has an elevated risk of depres-sion, psychosis, and stroke. Lack of sleep isalso directly tied to obesity: Without enoughsleep, the stomach and other organs overpro-duce ghrelin, the hunger hormone, causing usto eat more than we need. Proving a cause-and-efect relationship in these cases is challenging,because you can’t subject humans to the neces-sary experiments. But it’s clear that sleepless-ness undermines the whole body.Power naps don’t solve the problem; nor dopharmaceuticals. “Sleep is not monolithic,” saysJefrey Ellenbogen, a sleep scientist at JohnsHopkins University who directs the Sound SleepProject, which counsels businesses on how theiremployees can achieve better performancethrough healthier rest. “It’s not a marathon; it’smore like a decathlon. It’s a thousand diferentthings. It’s tempting to manipulate sleep withdrugs or devices, but we don’t yet understandsleep enough to risk artificially manipulatingthe parts.”Ellenbogen and other experts argue againstshortcuts, especially the original one—thenotion that we can mostly do without sleep.It was a glorious idea: If we could just cut theunnecessary parts of sleep, it’d be like addingdecades to our life. In the early days of sleepscience, the 1930s and ’40s, the second half ofthe night was considered by some to be the dol-drums of rest. Some thought we might not needit at all.That period turns out, instead, to be thewellspring of a completely separate but just asessential form of sleep, practically another typeof consciousness altogether.REMIN A WILD STATE OF PSYCHOSIS, WE’RE DREAMING,WE’RE FLYING, AND WE’RE FALLING—WHETHER WEREMEMBER IT OR NOT. WE’RE ALSO REGULATING OURMOOD AND CONSOLIDATING OUR MEMORIES.Rapid eye movement, or REM, sleep was discov-ered in 1953—more than 15 years after stages 1through 4 had been mapped—by Eugene Aserin-sky and Nathaniel Kleitman at the University ofChicago. Before then, because of its unremark-able pattern on early EEGs, this period wasusually thought of as a variant form of stage 1,and not particularly significant. But once thedistinctive eye darting was documented, andthe engorgement of sexual organs that alwaysgoes with it, and it was understood that virtuallyall vivid dreaming takes place in this phase, thescience of sleep was upended.Generally, a healthy sleep begins with a spiraldown to stage 4, a momentary return to wakeful-ness, and a five- to 20-minute REM session. Witheach ensuing cycle, REM time roughly doubles.Overall, REM sleep occupies about one-fifth oftotal rest time in adults. Yet stages 1 through 4have been labeled as non-REM sleep, or NREM—80 percent of sleep is defined by what it’s not.Sleep scientists speculate that specific sequencesof NREM and REM sleep somehow optimize ourphysical and mental recuperation. At the cellularlevel, protein synthesis peaks during REM sleep,keeping the body working properly. REM sleepalso seems essential for regulating mood andconsolidating memories.Every time we experience REM sleep, weliterally go mad. By definition, psychosis is acondition characterized by hallucinations anddelusions. Dreaming, some sleep scientists say,is a psychotic state—we fully believe that wesee what is not there, and we accept that time,location, and people themselves can morph anddisappear without warning.From ancient Greeks to Sigmund Freud toback-alley fortune-tellers, dreams have alwaysbeen a source of enchantment and mystery—interpreted as messages from the gods or ourunconscious. Today many sleep experts aren’tinterested in the specific images and events inour dreams. They believe that dreams result72 NATIONAL GEOGRAPHIC