97 Fun Facts About Sleep and Dreams

Roughly how long after falling asleep does the first REM episode begin?

70 minutes in, the first REM episode starts, and it is usually the shortest of the night at only a few minutes; a typical adult has four to five REM periods before waking.

During which stage of sleep does temporary muscle paralysis, known as atonia, typically occur?

REM atonia is a protective mechanism during rapid eye movement (REM) sleep that prevents individuals from physically acting out their vivid dreams.

In 2007 the American Academy of Sleep Medicine cut the NREM sleep stages from four to how many?

The old stages 3 and 4 were merged, so a modern sleep study reports three NREM stages plus REM.

Approximately how long does one complete sleep cycle typically last in adults?

An average sleep cycle, which includes all NREM and REM stages, lasts about 90 to 110 minutes, and most adults go through 4 to 6 cycles per night.

Which pair of EEG features is characteristic of NREM Stage 2?

Spindles and K-complexes: a K-complex is the single largest event in a healthy human EEG, and a sound or a touch can trigger one without waking the sleeper.

Which of these is secreted most heavily during NREM Stage 3, the deepest stage of the night?

Growth hormone: its largest pulse of the day comes during the slow-wave sleep of the first hours of the night, which is why deep sleep matters for tissue repair and growth.

REM sleep, the stage most associated with dreaming, takes up roughly what share of an adult's total sleep?

20–25% of an adult's sleep is REM, but newborns spend far more of their sleep in it, one reason researchers think it helps the developing brain.

As the night progresses, how does the proportion of REM sleep typically change within each sleep cycle?

Early sleep cycles have shorter REM periods and longer deep sleep, but as the night progresses, REM stages become progressively longer.

What other name is NREM Stage 3 sleep known by, thanks to its characteristic brain waves?

The presence of large, slow delta waves on an EEG during NREM Stage 3 leads to its alternative name, slow-wave sleep (SWS).

Which neurotransmitter is abundant during REM sleep while serotonin and norepinephrine are nearly absent?

Acetylcholine: cholinergic cells in the pons switch REM on while the serotonin and norepinephrine cells fall silent, and the missing norepinephrine is one reason dreams so rarely reach lasting memory.

What is the scientific study of dreams called?

Oneirology, from the Greek oneiros for dream, is the scientific study of dreams; dream interpretation itself dates back to the Sumerians and Babylonians in the third millennium BCE.

Roughly how much time does a human spend dreaming each night?

Individual dreams last around 5 to 20 minutes each.

Across Calvin Hall's 50,000-plus dream reports, which emotion turned up most often?

Anxiety was the most common emotion in Hall's dream reports, with negative emotions outnumbering positive ones overall; sexual dreams, by contrast, made up no more than 10% of reports.

Which phase of sleep did Aserinsky and Kleitman's 1953 paper establish and tie to dreams?

Their discovery, published in Science, was the turning point for modern dream research.

According to Freud, dreams serve what purpose for the sleeper?

Prolonging sleep by presenting wishes as fulfilled: Freud called dreams the guardians of sleep, disguised fulfilments of repressed wishes, and cared more about interpreting them than explaining how they arise.

In Greek myth, which god of dreams sent warnings and prophecies to people sleeping at shrines and temples?

Morpheus delivered his messages to sleepers at shrines; early Greeks believed gods entered a sleeper's room through the keyhole.

In 1964, 17-year-old Randy Gardner set a record by staying awake for roughly how long?

Eleven days: Gardner stayed awake 264 hours in January 1964 without stimulants, monitored by a Navy doctor and sleep researchers, and slept just under 15 hours once it was over.

Why did Guinness World Records stop accepting sleep-deprivation record attempts?

Safety reasons ended it: the record then stood at 18 days and 21 hours, held by Robert McDonald, after Randy Gardner's mark had been broken repeatedly.

Which mammal sleeps the longest, roughly 20 to 22 hours daily?

Koala: a diet of low-energy eucalyptus leaves keeps it dozing 20 to 22 hours a day, about as long as any mammal sleeps; bats are the only serious rival.

Which sleep pattern lets ducks at a flock's edge keep one eye open for threats?

Unihemispheric sleep: one half of the brain rests while the other stays alert, so ducks on the edge of a flock do more of it and react to threats seen by the open eye.

Horses can sleep standing up, but must lie down for short periods to get which kind of sleep?

REM brings muscular atony, so a standing animal would collapse.

Who coined the term 'lucid dream' in a 1913 article?

Frederik van Eeden coined 'lucid dream' in his 1913 paper A Study of Dreams, using 'lucid' in the sense of having insight, as in a lucid interval.

Lucid-dreaming pioneer Stephen LaBerge did his dream research at which Californian university?

Stanford: LaBerge earned his doctorate there and ran his lucid-dream studies in its sleep lab, finding that dream awareness and dream control are correlated but neither requires the other.

In narcolepsy, the sudden loss of muscle tone triggered by strong emotion is called what?

Cataplexy, the emotion-triggered loss of muscle tone, is the hallmark of type 1 narcolepsy, which is linked to low levels of the neuropeptide orexin in cerebrospinal fluid.

Which virus is thought to trigger the autoimmune process behind narcolepsy in susceptible people?

H1N1 influenza: narcolepsy cases rose after the 2009 H1N1 pandemic and the Pandemrix vaccine, and the resulting immune attack destroys the neurons that produce orexin.

Sleepwalking occurs during which stage of sleep?

Slow-wave NREM: sleepwalking is a partial arousal out of deep sleep, which is why it usually happens in the first third of the night, when deep sleep dominates.

What is the medical term for sleepwalking?

Somnambulism is also called noctambulism; its cousin somniloquy is sleep-talking, and bruxism is teeth-grinding.

One of the most common hallucinations during sleep paralysis is the presence of what?

An incubus pressing on the chest is the classic sleep-paralysis hallucination, often with a sensed presence in the room; between 8% and 50% of people experience sleep paralysis at some point.

The word 'circadian' derives from Latin words meaning what?

Approximately one day: circa diem, a term coined by Franz Halberg in 1959; external cues that reset the clock, such as light and temperature, are called zeitgebers.

In 1729, de Mairan showed an internal clock exists by keeping which plant in constant darkness?

Mimosa pudica: in constant darkness its leaves kept opening and closing on a roughly 24-hour pattern with no daylight cue, the first recorded evidence of an internal clock.

Aaron Lerner isolated melatonin from cow pineal glands in 1958 because it did what to frogs?

Lightened their skin: Lerner was chasing the pineal factor that blanched frog skin, which is how the hormone got its name; the body makes melatonin from the amino acid tryptophan, via serotonin.

The 'mare' in 'nightmare' originally referred to what in European folklore?

A demon that sits on sleepers' chests: the Old English mare was such a goblin, and the 1781 painting The Nightmare shows one crouched on a sleeping woman.

In a 2009 Pew survey, what fraction of American adults had napped in the past day?

One in three: 34% of US adults in Pew's 2009 survey had napped in the previous 24 hours; the grogginess right after waking from a nap is called sleep inertia.

Coffee and tea keep you awake by temporarily blocking the effect of which sleep-promoting molecule?

Adenosine builds up during waking hours, driving the pressure to sleep.

In a bunker with constant light or dark, a human's body clock settles on what period?

Slightly longer than 24 hours: free-running volunteers drift to a roughly 24.2-to-25-hour day, and daylight normally nudges the cycle back down to match Earth's rotation.

The siesta habit has been associated with roughly 37% lower mortality from which condition?

Coronary heart disease mortality was 37% lower among siesta-takers, possibly because daytime sleep reduces cardiovascular stress.

According to Aristotle, dreams were caused by what?

Processing incomplete physiological activity: Aristotle held that dreams arise from sense impressions lingering in the body during sleep, not from the gods; his teacher Plato thought dreams unleashed repressed desires such as incest and murder.

Which two mammals with low metabolic rates sleep only about 2 to 4 hours a day?

Elephants and giraffes both get by on roughly 2 to 4 hours a day, giraffes often in short bouts while standing; rats, with a high metabolic rate, sleep up to 14 hours.

Which French researcher coined the term 'paradoxical sleep' for the REM state?

Jouvet's Lyon lab showed in the late 1950s that the state arises in the brainstem, and he championed it as the brain's third mode alongside waking and slow-wave sleep.

Sleep pioneer Nathaniel Kleitman ran studies underground in which Kentucky landmark?

Mammoth Cave: in 1938 Kleitman and his student Bruce Richardson spent 32 days there trying to live a 28-hour day; he also studied sleep aboard submarines in World War II and above the Arctic Circle.

Which sleep scientist lost at pinball to Randy Gardner on day ten of his 1964 vigil?

Dement attended the teenager's record attempt while a Navy doctor monitored his health; Gardner stayed sharp enough to win games late in the ordeal.

Eugene Aserinsky discovered REM sleep in 1953 while a graduate student where?

Aserinsky made the discovery in Kleitman's Chicago lab, partly by watching the eyes of his own sleeping son.

In 1962 Michel Siffre spent about two months without clocks or daylight in what setting?

A cave in the Alps: inspired by the space race, Siffre lived 130 metres down in the Scarasson abyss on the French-Italian border, and later spent six months in a Texas cave.

The wake-promoting peptide orexin was discovered in 1998 in the brain of which animal?

Rat: both groups isolated the peptide from rat hypothalamus; one named it orexin for its appetite-stimulating effect, the other hypocretin for its hypothalamic origin.

The 2017 Nobel for circadian-rhythm discoveries rested on work in which organism?

Fruit flies: Hall, Rosbash and Young used Drosophila to show how the period gene's protein switches off its own production, creating a roughly 24-hour loop.

The brain's master body clock sits directly above which structure?

The optic chiasm: the suprachiasmatic nucleus sits right on top of it, so light information arrives straight from the retina, letting the clock reset itself to dawn and dusk.

The 'mela' in melatonin comes from the Greek word for which colour?

Black: melas is Greek for black, because Lerner named the hormone for its effect on the dark pigment melanin in frog skin, with the '-tonin' ending borrowed from serotonin, its chemical parent.

The brain's waste-clearing 'glymphatic' system takes its name from what?

Glial cells: the name fuses 'glia' with 'lymphatic', since glial cells line the channels that flush the brain; clearance of metabolic waste speeds up during slow-wave sleep, one reason sleep is thought restorative.

Fatal familial insomnia belongs to which class of disease?

Prion: fatal familial insomnia is an inherited prion disease driven by a single mutation at codon 178 of the PRNP gene; average survival after onset is about 18 months.

Kleine–Levin syndrome, with episodes of sleeping 15–21 hours, usually hits whom first?

Adolescents: onset is typically in the teenage years, mostly in boys; nicknamed 'Sleeping Beauty syndrome', it is marked by compulsive eating during episodes and usually fades out after a decade or so.

Who first described the 1917 'sleepy sickness' now called encephalitis lethargica?

Constantin von Economo presented the disease in Vienna in April 1917; the pandemic of the late 1910s and 1920s hit nearly 5 million people, and French physician Jean-René Cruchet published similar cases within days.

The CPAP machine for sleep apnoea was invented in 1980 in which city?

Sydney: Colin Sullivan built the first device at Royal Prince Alfred Hospital; early versions used a vacuum-cleaner motor blowing air through a mask.

Restless legs syndrome is also known by which eponym?

Willis–Ekbom disease: Thomas Willis described the condition in the 17th century and Karl-Axel Ekbom coined 'restless legs' in 1945; the urge to move eases with movement and peaks in the evening.

The Epworth Sleepiness Scale, launched in 1991, is named after a hospital in which city?

Melbourne: Murray Johns devised it at Epworth Hospital; the eight-question survey asks how likely you are to doze in everyday situations, such as sitting in traffic.

In Greek myth, Hypnos, god of sleep, had which twin brother?

Thanatos, god of death: the twins lived side by side in the underworld, where the sun's rays never reached them, so sleep and death were literally siblings.

In Homer's Odyssey, truthful dreams arrive through a gate made of what material?

Horn: Penelope says true dreams pass through the gate of horn and deceitful ones through the gate of ivory; Virgil reused the image, sending Aeneas out of the underworld by the ivory gate.

The dreamcatcher's Ojibwe name, asabikeshiinh, is the word for which creature?

The hoop and web were a protective charm for infants, linked to Asibikaashi, Spider Woman, who looked after children.

Washington Irving's Rip Van Winkle wakes from his mountain nap after how many years?

20 years: he sleeps through the entire American Revolution after drinking with mysterious Dutchmen in the Catskills, and wakes to find the inn sign's King George repainted as George Washington.

The Taoist philosopher Zhuang Zhou famously dreamed he was which creature?

A butterfly: waking, Zhuang Zhou could not say whether he was a man who had dreamed of being a butterfly, or a butterfly now dreaming of being a man.

August Kekulé said the ring structure of benzene came to him in a reverie about what?

The image is the ancient ouroboros; oddly, Kekulé had once testified in a murder trial about a ring showing two snakes biting each other's tails.

Otto Loewi's dream-inspired Nobel experiment used which organ taken from frogs?

Hearts: Loewi stimulated one frog heart's vagus nerve and showed its fluid slowed a second heart, proving chemical transmission; he scribbled the idea on his night-stand, could not read it next morning, and waited for the dream to return.

Coleridge said his dream-poem Kubla Khan was cut short by a visitor from which village?

The opium-tinged vision came after reading about Xanadu; the 'person on business from Porlock' is now shorthand for any unwelcome interruption.

Which Robert Louis Stevenson story took its central idea from a dream he had?

Dr Jekyll and Mr Hyde: his wife woke him mid-nightmare, he complained she had interrupted 'a fine bogey tale', and he wrote the first draft in about three days.

Paul McCartney dreamed the melody of 'Yesterday'; what was the song's working title?

Scrambled Eggs: the tune arrived at Jane Asher's family home on Wimpole Street, and McCartney sang 'Scrambled eggs, oh my baby how I love your legs' while spending weeks checking he hadn't copied it.

Keith Richards woke to find he had taped the riff of which song in his sleep?

Satisfaction: the cassette held two minutes of the '(I Can't Get No) Satisfaction' riff, the sound of the pick dropping, and then forty minutes of snoring.

Stephenie Meyer's dream on 2 June 2003 became which numbered chapter of Twilight?

13: the meadow scene, where Edward shows Bella his skin in sunlight, became Chapter 13; Meyer had no writing experience and wrote the rest of the book outward from it.

Freud's The Interpretation of Dreams was first printed in an edition of how many copies?

Those 600 took eight years to sell out, though the book was dated 1900 to mark the new century.

Artemidorus' 2nd-century dream manual, the Oneirocritica, survives in how many books?

Five: the first three books were for the public, while the last two were written for his son, with a warning against letting rivals copy them.

Who coined 'hypnopompic' for the hazy state of waking up?

Frederic Myers coined it, ending with the Greek for 'sender' to pair with 'hypnagogic', Alfred Maury's 1848 term for the drift into sleep.

Which parasomnia did a British psychiatrist describe in 1920 as 'snapping of the brain'?

Exploding head syndrome: sufferers hear a gunshot, firework or scream nobody else does as they fall asleep or wake; psychiatrist Robert Armstrong-Jones coined 'snapping of the brain' in 1920.

REM sleep behaviour disorder, in which people act out dreams, strongly predicts what?

Parkinson's disease: acting out dreams is one of the earliest warning signs of the synucleinopathies, Parkinson's and Lewy-body dementia, sometimes appearing a decade or more before tremor.

Most travellers find jet lag harder after flying in which direction?

East: because the body clock runs slightly longer than 24 hours, delaying bedtime after a westward flight comes more naturally than advancing it after an eastward one.

Pods of sperm whales have been seen napping in what unusual position?

Vertical, heads near the surface: a 2008 study found pods drifting upright like giant logs, possibly in deep sleep for about 7 percent of the time, mostly between 6 p.m. and midnight.

Non-breeding common swifts may stay airborne for up to how many months without landing?

Ten: a 2016 tracking study found some swifts stayed aloft for ten months straight; they never settle on the ground voluntarily and appear to sleep on the wing during slow glides at altitude.

In hibernation, an Arctic ground squirrel's heart slows to about how many beats a minute?

1: its heart slows from around 200 beats a minute to roughly one, and its core temperature drops to −2.9 °C, the lowest recorded in any mammal, without its blood freezing.

DJ Peter Tripp's 201-hour 1959 'wakeathon' was staged in a glass booth where?

Times Square: Tripp broadcast from a glass booth there for a March of Dimes stunt; he began hallucinating after a few days, and doctors drugged him to stay awake for the last 66 hours.

Which Swiss-born artist's 1781 painting The Nightmare became his first commercial success?

Henry Fuseli: the canvas shows a ghostly horse peering through curtains while a crouching demon sits on a sleeping woman; it caused a sensation at the Royal Academy in 1782.

Which historian argues pre-industrial Europeans slept in 'first' and 'second' sleeps?

Roger Ekirch, in At Day's Close (2005), assembled hundreds of references to a waking hour around midnight used to pray, reflect and interpret dreams, which were more vivid then than in the morning.

In which country is dozing in a meeting traditionally read as proof of hard work?

Japan: the custom is called inemuri, roughly 'sleeping while present', and dozing in a meeting can read as proof you worked to exhaustion.

The word 'siesta' derives from a Latin phrase meaning which hour of the day?

Counted from dawn, hora sexta lands around noon, when Romans along the Mediterranean took their midday rest.

In a 2000 study, amnesiacs dreamed of which video game they could not remember playing?

Tetris: the amnesiacs reported falling blocks at sleep onset, which Robert Stickgold's team took as evidence that the 'Tetris effect' runs on procedural memory, not conscious recollection.

Keith Hearne recorded the first signals sent from inside a lucid dream using what?

His subject, Alan Worsley, performed a pre-agreed eye sequence that showed up on the electrooculogram while he was measurably asleep.

On 10–11 November 1619, which philosopher had three dreams he took as a divine calling?

René Descartes: a soldier shut in a stove-heated room at Neuburg an der Donau, he read the dreams as a call to found a new science, and later used dreaming to ask whether anything can be known for certain.

Dallas wrote off its entire ninth season as the dream of which character?

Pam Ewing: the twist brought her husband Bobby back from the dead; he reappeared in her shower as if the whole year had never happened.

Zolpidem, approved for US use in 1992, is best known under which brand name?

Ambien: zolpidem is linked to complex sleep behaviours such as sleep-driving, and in 2013 the FDA advised against activities needing full alertness the day after extended-release doses.

Sleeping sickness, African trypanosomiasis, is spread by the bite of which insect?

Tsetse fly: its bite passes on the parasite Trypanosoma brucei, which eventually invades the brain, scrambling the sleep-wake cycle that gives the disease its name.

Michael Stipe chose the band name R.E.M. how?

At random from a dictionary: Stipe landed on the abbreviation while flipping through one; rejected alternatives included 'Twisted Kites', and the band never claimed the name was about rapid eye movement.

In Genesis, which Hebrew prisoner interpreted Pharaoh's dream of seven lean cows devouring seven fat ones?

Joseph read it as seven years of plenty then seven of famine, and the interpretation made the Hebrew prisoner second-in-command of Egypt.

The word 'cemetery' comes from a Greek word meaning what?

Sleeping place: koimeterion, from the Greek for putting to sleep, was first applied by early Christians to the Roman catacombs, casting the dead as merely asleep.

Who recorded the first human EEG, the tool later used to map sleep stages, in 1924?

Hans Berger, a psychiatrist in Jena, recorded the first human EEG in 1924 and named the alpha wave; he was partly motivated by a belief in telepathy.

Which chemist claimed the complete periodic table came to him in a dream?

Dmitri Mendeleev said he saw in a dream a table where every element fell into place as required, wrote it down on waking, and claimed only one correction was later needed.

In R v Parks (1992), what verdict did Canada's top court uphold for a sleepwalking killer?

Acquittal: Kenneth Parks drove 20 km, attacked his in-laws, then drove to a police station with no memory of it; the court treated sleepwalking as non-insane automatism, so the acquittal stood.

In which country is sleep paralysis known as 'the ghost pushes you down'?

Cambodians link the episodes to visits from dead relatives; in Japan the same experience is called kanashibari, roughly 'bound in metal'.

'Ondine's curse' is an old name for a condition in which sleepers stop doing what?

Breathing: the name comes from a water nymph's curse that her faithless lover would forget to breathe if he ever slept; the modern term is congenital central hypoventilation syndrome.

Veronal, sold as a sleeping aid from 1903, was the first commercially available what?

Barbiturate: Emil Fischer and Joseph von Mering synthesised barbital, and Bayer sold it as Veronal for 'insomnia induced by nervous excitability'.

Francis Crick and Graeme Mitchison's 1983 theory held that we dream in order to do what?

Forget: their 'reverse learning' model treats REM as the brain offline, damping down unwanted connections like a computer clearing junk, hence their slogan 'we dream in order to forget'.

Which Shakespeare character is watched wandering asleep by a doctor and a gentlewoman?

Lady Macbeth: the scene opens Act V at Dunsinane, with her trying to wash imagined blood from her hands while the Doctor and Gentlewoman look on.