National Geographic

sleep, whether snoring or not, we’re completelyincapable of physical response, slack-jawed,unable to regulate even our blood pressure. Yetour brain is able to convince us that we’re surfingon clouds, slaying dragons.Belief in the unbelievable happens becausein REM sleep, stewardship of the brain istransferred away from the logic centers andimpulse-control regions. Production of twospecific chemicals, serotonin and norepineph-rine, is completely shut of. Both are essentialneurotransmitters, permitting brain cells tocommunicate, and without them, our ability tolearn and remember is severely impaired—we’rein a chemically altered state of consciousness.But it’s not a coma-like state, as in stage 4. Ourbrain during REM sleep is fully active, guzzlingas much energy as when we’re awake.REM sleep is ruled by the limbicsystem—a deep-brain region, theuntamed jungle of the mind, wheresome of our most savage and base instincts arise.Freud was right, in efect, that dreams do tap ourprimitive emotions. The limbic system is hometo our sex drive, aggression, and fear, though italso allows us to feel elation and joy and love.``````While it sometimes seems as if we have morenightmares than pleasant dreams, this probablyisn’t true. Frightening dreams are simply morelikely to trigger our override system and wake us.Down in the brain stem, a little bulge calledthe pons is supercharged during REM sleep.Electrical pulses from the pons often target thepart of the brain that controls muscles in theeyes and ears. Our lids usually remain shut, butour eyeballs bounce from side to side, possiblyin response to the intensity of the dream. Ourinner ears too are active while we dream.from the chaotic firing of neurons and, even ifimbued with emotional resonance, are devoid ofsignificance. It’s only after we wake that the con-scious brain, seeking meaning, quickly stitchestogether a whole cloth out of haphazard scraps.Other sleep scientists strongly disagree. “Thecontent of dreams,” says Stickgold of Harvard,“is part of an evolved mechanism for looking atthe larger significance of new memories and howthey could be useful in the future.”Even if you never recall a single image, youstill dream. Everyone does. Lack of dream rec-ollection is actually an indication of a healthysleeper. The action in dream sleep takes placetoo deep in the brain to register well on an EEG,but with newer technology, we’ve inferred what’sgoing on, physically and chemically. Dreamsalso occur in NREM sleep, especially stage 2,but these are generally thought to be more likeovertures. Only in REM sleep do we encounterthe full potent force of our nighttime madness.Dreams, often falsely said to be just momen-tary flashes, are instead thought to span almostall of REM sleep, typically about two hours pernight, though this decreases as we age—perhapsbecause our less pliant brains are not learning asmuch while awake and have fewer new memo-ries to process as we sleep. Newborninfants sleep up to 17 hours a dayand spend about half of that in anactive, REM-like condition. And forabout a month in the womb, startingat week 26 of gestation, it seems thatfetuses remain without pause in astate very similar to REM sleep. Allthis REM time, it has been theorized,is the equivalent of the brain testingits software, preparing to come fullyon line. The process is called telen-cephalization. It’s nothing less thanthe opening of the mind.The body doesn’t thermoregulate in REMsleep; our internal temperature remains at itslowest setting. We are truly out cold. Our heartrate increases compared with other sleep stages,and our breathing is irregular. Our muscles,with a few exceptions—eyes, ears, heart, dia-phragm—are immobilized. Sadly, this doesn’tkeep some of us from snoring; this bane of thebed partner, impetus for hundreds of anti-snoring gadgets, is caused when turbulent air-flow vibrates the relaxed tissues of the throat ornose. It’s common in stages 3 and 4 too. In REMEvery time we experience REMsleep, we literally go mad. Psychosisis a condition characterized byhallucinations and delusions.Dreaming, some sleep scientists say,is a psychotic state—we fully believethat we see what is not there, andwe accept that time, location, andpeople can morph and disappear.SLEEP 73