127 Fun Facts About Sleep and Dreams

Slipping into REM within minutes of dozing off is a hallmark of which disorder?

Narcolepsy: most sleepers take an hour or more to reach REM, but people with narcolepsy often enter it within 15 minutes, which is why dream imagery and muscle weakness can spill into their waking hours.

Which colour of light, plentiful in phone and laptop screens, does most to delay the body's night-time sleep signal?

Blue: in a Harvard experiment it shifted the body clock about twice as far as green light, while dim red light disturbs the clock least, so red suits a night light.

Which inventor is said to have napped with a ball in each hand, so that the clatter cut each nap short?

Thomas Edison is said to have prized the ideas that surface at the edge of sleep, and a 2021 study backs him: as little as 15 seconds of that drowsy state nearly tripled volunteers' chances of cracking a hidden maths rule.

Roughly how long does one full cycle of adult sleep last?

About 90 minutes: sleep pioneer Nathaniel Kleitman argued the same rhythm keeps ticking through the day, nudging alertness up and down roughly every hour and a half.

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 arrives about an hour after sleep begins, in the first stretch of deep sleep, which is why that stage matters for tissue repair and growth.

Which age group spends the largest share of its sleep in REM?

Newborn babies spend far more of their sleep in REM than adults do, and the share falls as they grow; one theory is that REM supplies the stimulation a developing brain needs to wire itself.

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

It lengthens: the first REM period may last only a few minutes, while later ones can run for around an hour, so most of the night's REM, and its dreams, comes in the hours before waking.

What other name do sleep scientists use for NREM Stage 3?

Slow-wave sleep is named for the large, slow delta waves that sweep the brain in this stage; it is the hardest sleep to wake from, so an alarm that catches you in it leaves you groggy.

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

Acetylcholine: cholinergic cells in the brainstem switch REM on while the serotonin and norepinephrine cells fall almost silent, and the missing norepinephrine is thought to be one reason dreams fade so fast.

What is the scientific study of dreams called?

Oneirology asks how the brain produces dreams, measuring the process rather than decoding meanings; that second job, dream interpretation, is a far older craft the Babylonians were already practising.

Added up over a whole night, roughly how long does a typical person spend dreaming?

About 2 hours: the night's dreaming comes in episodes of roughly 5 to 20 minutes each, far more than most people would guess, because nearly all of it has faded by morning.

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

Anxiety topped Hall's tally, and negative emotions as a whole outnumbered positive ones; he gathered the reports from children, older adults and people around the world, then coded their content by category.

Which Gothic novel grew from a 'waking dream' its 18-year-old author had beside Lake Geneva in 1816?

Frankenstein: challenged by Lord Byron to write a ghost story, Mary Shelley lay awake one night and saw a 'pale student of unhallowed arts' kneeling beside the thing he had put together.

According to Freud, what purpose do dreams serve?

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.

Which god of dreams, in Ovid's telling, takes human form to carry messages to sleepers?

Morpheus, one of the thousand sons of Sleep in Ovid's Metamorphoses, could copy any person's walk, face and voice; centuries later his name supplied the word morphine.

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

Eleven days: Gardner stayed awake 264 hours for a school science fair on nothing stronger than the occasional Coke, then slept for only about 14 hours before waking naturally.

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

Safety reasons: Guinness stopped monitoring the record in 1997, which froze Robert McDonald's 1986 run of 18 days 21 hours as its last official mark; nobody is known to have beaten it since.

Which leaf-eating mammal sleeps for up to 20 hours a day?

Koala: eucalyptus leaves are tough, toxic to most mammals and poor in calories, so the koala saves energy by sleeping up to 20 hours a day, often in the same tree it feeds in.

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.

Which marine mammal wraps itself in kelp so it will not drift away while it rests?

Sea otter: anchoring itself in kelp stops the current carrying it off as it rests at the surface, and a mother will wrap her pup in kelp so it bobs like a cork while she dives for food.

Dutch psychiatrist Frederik van Eeden coined which dream term in 1913?

Lucid dream: van Eeden meant 'lucid' as clear-minded, not vivid; in such a dream, he wrote, the sleeper reaches full awareness and can act by free choice.

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

Stanford: LaBerge earned his doctorate there in 1980 for lucid-dream research, devised the MILD technique for entering one at will, and went on to found the Lucidity Institute to teach it.

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.

Sleepwalkers are not acting out their dreams; in which stage of sleep does sleepwalking usually begin?

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: if you meet a sleepwalker, the advice is to steer them gently back to bed, because someone woken suddenly from it is confused and may be frightened or angry.

Which bringer of sleep is named in the titles of a Metallica hit and a Neil Gaiman comic series?

The Sandman: in folklore he sends children to sleep by sprinkling sand in their eyes, but in the German writer Hoffmann's tale of the same name a nurse describes a monster whose sand makes wakeful children's eyes fall out.

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

Approximately one day: Franz Halberg coined 'circadian' in 1959 from the Latin circa, 'around', and dies, 'day', choosing 'about' because the body's rhythms run close to 24 hours without always matching it.

In 1729, de Mairan found which leaf-folding plant kept its daily rhythm even in constant darkness?

Mimosa pudica: shut away from daylight, its leaves still opened by day and folded at dusk, the first recorded hint of a body clock, though de Mairan himself stopped short of that conclusion.

Dermatologist Aaron Lerner isolated which hormone in 1958 while hunting the pineal extract that lightened frog skin?

Melatonin: it blanches frog skin, yet in people its job turned out to be sleep, because the brain releases it as darkness falls and so tells the body's clock that night has come.

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.

What do sleep scientists call the groggy, slow-witted spell that follows waking, often worst after a long nap?

Sleep inertia usually clears within an hour, but it bites hardest when you are woken out of deep sleep, which is why naps kept under half an hour tend to leave people sharper.

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.

A 2007 study of Greek adults linked regular siestas to 37% lower mortality from which condition?

Coronary heart disease: regular nappers had a 37% lower coronary death rate, and the link was strongest among working men, possibly because a midday rest eases stress on the heart.

According to Aristotle, what gives rise to dreams?

Lingering traces of waking sensations: Aristotle likened them to the little eddies that keep swirling in a river, movements left in the sense organs that surface once sleep quietens everything else.

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.

Michel Jouvet gave REM which name, because the brain looks awake while the body lies limp?

Paradoxical sleep: Jouvet's cats showed waking-style brain activity while their muscles went slack, and when he damaged the brainstem area behind that paralysis they moved as if acting out a dream.

Sleep pioneer Nathaniel Kleitman spent more than a month underground in which US cave to study the body's daily rhythms?

Mammoth Cave: in Kentucky, with no sunlight to set their clocks, Kleitman and an associate charted how their wakefulness and body temperature rose and fell; he later took the same questions aboard a submarine.

Late in his 1964 record without sleep, teenager Randy Gardner still beat sleep researcher William Dement at which game?

Pinball: Dement reported losing to the sleepless teenager, even though the Navy doctor monitoring Gardner was logging moodiness, memory lapses and trouble concentrating by then.

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

University of Chicago: working in Nathaniel Kleitman's lab there, Aserinsky spent hours watching the eyelids of sleeping volunteers, then showed with Kleitman that the twitching went hand in hand with dreaming.

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

A cave in the Alps: Siffre camped in the Scarasson abyss, and when his team called him up on 14 September he believed it was only 20 August, with weeks of his stay still to run.

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, the root it shares with melanin, the body's dark pigment, and with melancholy, a gloom once blamed on an excess of 'black bile'.

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

Glial cells: the name fuses 'glia' with 'lymphatic', as glial cells run the channels that rinse the brain; a 2013 mouse study found the rinse speeds up in sleep, though a 2024 study reported the opposite.

Fatal familial insomnia belongs to which class of disease?

Prion: misfolded prion protein builds up in the thalamus, a deep brain hub that helps regulate sleep, and kills its nerve cells, so sufferers steadily lose the ability to sleep at all.

Kleine–Levin syndrome, with episodes of sleeping up to 20 hours a day, 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.

Which neurologist revived survivors of the 1920s 'sleepy sickness' with the drug L-dopa?

Oliver Sacks gave L-dopa in the late 1960s to patients left statue-like for decades by encephalitis lethargica; they woke dramatically, but for most the effect was temporary, as his book Awakenings records.

Sleep bruxism is the medical name for doing what during the night?

Grinding your teeth: the word comes from the Greek for 'to gnash', and stress is often linked to it, so a tense week may show up as an aching jaw first thing in the morning.

Willis–Ekbom disease names which condition that flares in the evening?

Restless legs syndrome: Thomas Willis described it in 1672 and Karl-Axel Ekbom named it in 1945; walking brings only temporary relief, so sufferers may pace the floor when they most want to sleep.

What term do sleep researchers use for a person's built-in tendency to be a morning lark or a night owl?

Chronotype: it is driven by the body clock and partly inherited, and it shapes more than bedtime, influencing appetite and core body temperature across the day as well.

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

Thanatos, god of death: in the Iliad the twin brothers Sleep and Death together carry the slain hero Sarpedon home from Troy to Lycia, a scene Greek vase painters returned to again and again.

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 General 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?

A snake biting its tail: Kekulé said he dozed by the fire and saw chains of atoms writhe like snakes until one seized its own tail; he told the story 25 years after the discovery, and some historians doubt it.

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.

A 2003 dream of a vampire in a meadow became which novel?

Twilight: Stephenie Meyer, who had never written a novel, wrote the dream down on waking; it became Chapter 13, and she finished the story from there before going back to fill in the first twelve chapters.

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

600: that first printing took eight years to sell out, and although the book came out in 1899 its title page was dated 1900.

'To sleep, perchance to dream' is a line from which Shakespeare play?

Hamlet: in the 'To be, or not to be' soliloquy the prince pictures death as a welcome sleep, then recoils at what dreams might come in it: 'Ay, there's the rub.'

'Hypnagogic' describes the drift into sleep; which matching word describes the haze of waking up?

Hypnopompic: Frederic Myers built it on a Greek word for sending, as if sleep were seeing you off; a vision that lingers as you wake is a hypnopompic hallucination.

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

Exploding head syndrome: sufferers hear a bang like a gunshot or an explosion as they drift off or wake, yet, despite the alarming name, there is no pain and it is considered harmless.

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: flying east shortens your day and asks the body clock to shift earlier, and most people find it harder to fall asleep early than to stay up late, as a westward trip requires.

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.

Which bird eats, mates and even sleeps on the wing?

Common swift: it comes down almost only to nest, and outside the breeding season some stay airborne for ten months without settling once.

Which hibernating mammal lets its body cool to almost −3 °C without freezing?

Arctic ground squirrel: its core drops to −2.9 °C, yet through the winter it repeatedly rouses itself, warming up to normal body temperature and then cooling down again.

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 caused a sensation at the Royal Academy in 1782 and proved so popular that he painted at least three more versions; a print of it later hung in Sigmund Freud's Vienna apartment.

What did historian Roger Ekirch find that many pre-industrial Europeans did around midnight?

Woke between two sleeps: Ekirch gathered more than 500 references to a 'first sleep' and a 'second sleep', with an hour or two between them spent praying, visiting neighbours or making love.

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

Japan: the custom is inemuri, literally being present while asleep, and it is tolerated as a sign of working to exhaustion so long as the doze disturbs nobody and you can rejoin when needed.

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

The sixth: Romans counted the hours from sunrise, so the sexta hora fell at midday; oddly, English 'noon' comes from their ninth hour, about 3 pm, which later slid back to twelve.

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?

Eye movements: the eyes stay free to move in REM while the rest of the body lies paralysed, so in April 1975 Hearne's subject Alan Worsley flicked his in a pre-agreed pattern from inside a dream.

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

René Descartes: a soldier sheltering from the cold in a stove-heated room in southern Germany, he read the dreams as a call to reform all knowledge, and later used dreaming to ask whether anything can be known for certain.

The TV drama '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 picked the entry after the band had weighed up names such as 'Twisted Kites'; the letters are the standard abbreviation for rapid eye movement, the dreaming stage of sleep.

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.

Hans Berger, who recorded the first human EEG in 1924, began the work after an experience he took for what?

Telepathy: as a young soldier Berger was nearly crushed by a horse-drawn cannon, and his sister, many kilometres away, sensed danger and had their father telegraph him; he spent his career hunting the brain's 'psychic energy'.

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 to his in-laws' home, attacked them, then went to a police station saying he thought he had killed two people; the court treated sleepwalking as non-insane automatism, so the acquittal stood.

Which guest at the Mad Hatter's tea party in Alice's Adventures in Wonderland keeps falling asleep?

The Dormouse: it dozes between the Hatter and the March Hare, who rest their elbows on it, pour hot tea on its nose and are last seen trying to stuff it into the teapot.

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

Breathing: the name comes from the 1938 play Ondine, in which a water spirit's unfaithful husband finds his body no longer breathes by itself: 'a single moment of inattention and I forget to breathe.'

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.

Which Christopher Nolan film about thieves who raid sleeping minds grew from a treatment based on lucid dreaming?

Inception began as an 80-page treatment about 'dream stealers' that Nolan showed Warner Bros. after finishing Insomnia. He first pictured it as a horror film.

What do sleep researchers call a vivid dream of getting up and starting the day while still asleep in bed?

False awakening and lucid dreaming often turn up on the same night, and one can tip over into the other. Bertrand Russell said he had about a hundred in a row while coming round from an anaesthetic.

Dream yoga, a discipline for staying aware while asleep, belongs to the Buddhist tradition of which Himalayan region?

Tibet's Buddhist and Bon traditions teach dream yoga, known as milam, as a way to see that dreams are empty and to carry that insight into the daytime.

In which Tom Cruise film does a firm called Life Extension keep a frozen client in a lucid dream?

Vanilla Sky is named after the skies in certain Claude Monet paintings. It remakes the 1997 Spanish film Open Your Eyes, and Penélope Cruz plays the same role in both.

Research on lucid dreaming has found the dreams come more often to people with years of practice in what?

Meditation veterans report more lucid dreams than other people, and lucid dreaming itself has been described as a hybrid state with features of both waking and dreaming.

When lucid dreamers signalled the start and end of a ten-second count, dream time ran at what pace?

About the same as waking time: in Stephen LaBerge's 1985 pilot study, a dreamed ten-second count took roughly ten real seconds. Dreamed squats, though, took longer than real ones.

In a 2021 study at four labs, sleeping lucid dreamers correctly answered what kind of question put to them mid-dream?

Simple sums were solved by people confirmed to be in REM sleep, who could also follow instructions and answer yes-or-no questions. Teams in the US, France, Germany and the Netherlands pooled their results.

Which brain region, quiet in ordinary REM sleep, is better connected to other areas in frequent lucid dreamers?

The prefrontal cortex is where working memory happens, and neuroscientist Allan Hobson suggested its reawakening is the moment a dreamer recognises the dream for what it is.

Which London diarist recorded in August 1665 a dream in which he realised he could not be awake?

Samuel Pepys never meant the dream, or anything else in his diary, for his contemporaries' eyes: he wrote in shorthand, slipping into Spanish, French and Italian for the most private parts.

In MILD, the lucid-dreaming method devised by psychologist Stephen LaBerge, what does the letter M stand for?

Mnemonic induction of lucid dreams, MILD for short, is the best known of the techniques LaBerge built so that he and other researchers could become lucid at will.

Which sea creature ripples through skin-colour changes in a one-minute 'active sleep' stage that resembles REM?

The octopus also moves its eyes and body more and breathes faster in that stage, giving it a two-part sleep much like the REM and non-REM pattern of vertebrates.

Harvard psychologist Deirdre Barrett collected over 15,000 dream reports to study the effect of which world event?

The COVID-19 pandemic made dreams darker: themes of fear, illness and death turned up two to four times as often as before it began.

Which Australian mammal has the most REM sleep of any creature studied, yet probably does not dream?

The platypus spends more time in REM than any other creature known, but the electrical activity never reaches its forebrain, which suggests no dreams come with it.

A 2008 Dundee study linked colourless dreams to childhoods spent with the monochrome version of what?

Television in its monochrome era seems to have left a mark: older adults raised on it reported colourless dreams about five times as often as the younger adults tested.

Pavor nocturnus, which mostly strikes children and is not the same as a bad dream, is better known as what?

Night terrors are classed as a parasomnia and bring sudden terror or dread, whereas a nightmare is a bad dream that leaves fear or horror behind.

For an early dream study, psychologist Mary Whiton Calkins woke herself at different hours using what?

Alarm clocks let Calkins catch 205 dreams in seven weeks, each written on a notepad kept by the bed. She later became the first woman to lead the American Psychological Association.

Finnish scientist Antti Revonsuo argued that dreaming evolved to give people practice at doing what?

Facing danger in a dream works like a fire drill in Revonsuo's threat simulation theory: ancestors who rehearsed fight or flight overnight were better prepared for the real thing.

Sleep-lab studies by David Foulkes found preschoolers' dreams are mostly still images, often of what?

Animals feature in those static pictures; Foulkes found that story-like dreams, with the dreamer as an actor, only begin between the ages of 7 and 9.

Neuroscientist David Eagleman's 2021 theory says dreams exist to protect the brain territory of which sense overnight?

Vision goes idle in the dark, and the theory holds that dreaming keeps the occipital lobe busy so that the other senses cannot take over its unused territory.

Which 1977 theory by Harvard's Allan Hobson and Robert McCarley ties dreams to REM signals from the brainstem?

Activation-synthesis holds that the stirring of the brain in REM comes first and the dream is assembled from it afterwards. The theory first appeared in the American Journal of Psychiatry.

In which Roald Dahl book does a giant collect dreams in jars and give the good ones to sleeping children?

The BFG catches his dreams in Dream Country and destroys the bad ones, and the suitcase and trumpet he carries are the tools of that trade.

In Genesis, who dreams of a ladder reaching to heaven while sleeping with a stone for a pillow?

Jacob had the dream while fleeing his brother Esau, with angels going up and down the ladder. On waking he named the place Bethel, 'house of God'.

Which US president reportedly described a dream of mourning in the White House three days before his death?

Abraham Lincoln told the dream to his bodyguard Ward Hill Lamon, then added that in it some other fellow, not he, had been the one killed.

Whose wife Calpurnia is said to have begged him to stay home after dreaming of his murder?

Julius Caesar at first agreed to stay away from the Senate, but one of the conspirators talked him round and he was killed there. Calpurnia had dreamed of him dying in her arms.

In the Bible, which prophet explains King Nebuchadnezzar's dream of a huge statue with feet of iron and clay?

Daniel describes a statue with a head of gold, arms of silver, belly of bronze and legs of iron, shattered by a rock that grows into a mountain filling the whole earth.

Which Swiss psychiatrist, once seen by Freud as his heir, said dreams draw on a 'collective unconscious'?

Carl Jung held that figures such as the shadow or an old man appear in dreams as shared archetypes, and he warned against decoding symbols without knowing the dreamer's own situation.

A satyr dancing on a shield, dreamed during the siege of Tyre, was read as a victory omen for which conqueror?

Alexander the Great got a pun for an answer: in Greek, 'satyr' splits into sa Tyros, 'Tyre will be thine'. Freud later cited the story to show that dreams can be read like a rebus.

Which Roman emperor is said to have marked his soldiers' shields with a Christian sign after a dream before battle?

Constantine won the Battle of the Milvian Bridge in 312, and the sign on the shields is said to have been the Chi Rho, the first two letters of Christ's name in Greek.

Which Surrealist painter designed the dream sequence in Alfred Hitchcock's psychoanalysis thriller Spellbound?

Salvador Dalí and Hitchcock conceived a sequence so long and complicated that producer David O. Selznick cut most of what had been filmed.

Freud called the dream a sleeper remembers its 'manifest' content; which word did he use for the hidden meaning?

Latent content, in Freud's scheme, is disguised by 'dream-work', which condenses several ideas into one image and shifts feelings onto harmless objects.