fracture stages

comedian mike birbiglia was having troublewith sleep. though not with the actual sleeping part -- onenight, while staying in a hotel, he dreamed that a guided missile was on its way to hisbed, and in his dream, he jumped out the window to escape it. unfortunately, he also did this not in hisdream. from the second floor. and the window wasnot open. this little episode cost him 33 stitches anda trip to a sleep specialist. mike now sleeps in zipped-up mummy bags forhis own safety. the lesson here? sleep is not some break timewhen your brain, or your body, just goes dormant.

far from it. in truth, sleep is just anotherstate of consciousness. and only in the past few decades have we begun to really plumbits depths -- from why we sleep in the first place, to what goes on in our brains whenwe do, to what happens when we can’t sleep. and there is a lot that science has to sayabout your dreams! talk about weird! it’s like sigmund freudmeets neil gaiman. so, even though it may seem like you’redead to the world, when you sleep, your perceptual window remains slightly open. and kinda like mike birbiglia’s hotel roomwindow, a trip through it can make for a pretty wild ride.

but for your safety and enjoyment, i’m hereto guide you through this state of consciousness, where you’ll learn more than a few thingsabout human mind, including your own. and here’s hoping you won’t need any stitcheswhen we’re through. [intro] technically speaking, sleep is a periodic,natural, reversible and near total loss of consciousness, meaning it’s different thanhibernation, being in a coma, or in say, an anesthetic oblivion. although we spend about a third of our livessleeping, and we know that it’s essential to our health and survival, there still isn’ta scientific consensus for why we do it.

part of it probably has to do with simplerecuperation, allowing our neurons and other cells to rest and repair themselves. sleepalso supports growth, because that’s when our pituitary glands release growth hormones,which is why babies sleep all the time. plus, sleep has all kinds of benefits for mentalfunction, like improving memory, giving our brains time to process the events of the day,and boosting our creativity. but even if we’re not quite sure of allthe reasons why we sleep, technology has given us great insight into how we sleep. and for that we can thank little armond aserinsky.one night in early 1950s chicago, eight-year-old armond was tucked into his bed by his father.but this night, instead of getting a kiss

on the forehead, little armond got some electrodestaped to his face. armond’s dad was eugene aserinsky, a gradstudent looking to test out a new electroencephalograph, or eeg machine, that measures the brain’selectrical activity. that night, as his son slept peacefully, hewatched the machine go bonkers with brain wave patterns, and -- after making sure thathis machine wasn’t somehow broken -- discovered that the brain doesn’t just "power down"during sleep, as most scientists thought. instead, he had discovered the sleep stagewe now call rem or rapid eye movement, a perplexing period when the sleeping brain is buzzingwith activity, even though the body is in a deep slumber.

aserinsky and his colleague nathaniel kleitmanwent on to become pioneers of sleep research. since then, sleep specialists armed with similartechnology have shown that we experience four distinct stages of sleep, each defined byunique brainwave patterns. say you’re just going to bed. all day yourendocrine system has been releasing “awake” hormones like cortisol. but with nightfallcomes the release of sleepy melatonin hormones from the pineal gland. your brain is relaxed,but still awake, a level of activity that eegs measure as alpha waves. you’re feeling sleepy, your breath slows,and suddenly you’re asleep. this exact moment is clearly evident on an eeg reading, as thosealpha waves immediately transition to the

irregular non-rapid eye movement stage one(nrem-1) waves. it’s in this first stage of sleep you might experience hypnagogic sensations-- those brief moments when you feel like you’re falling, and your body jerks, startlingyou. as you relax more deeply, you move into nrem-2stage sleep, as your brain starts exhibiting bursts of rapid brain wave activity calledsleep spindles. you’re now definitely asleep, but you could still be easily awakened. nrem-3 comes with slow rolling delta waves.we now know that you can have brief and fragmentary dreams in the first three stages of sleep,but eventually you’ll get to the most important stage: full rem sleep, that famous stage ofsugarplum slumber that makes eyeballs go nuts,

grants vivid visual dreams, and provided thenamesake for a certain famous rock band. rem sleep is kinda paradoxical. your motorcortex is jumping all over the place, but your brainstem is blocking those messages,leaving your muscles so relaxed that you’re basically paralyzed. except for your eyes.that whole sleep cycle repeats itself every 90 minutes or so, transitioning back and forthbetween the stages of sleep. obviously sleep is super important, and lackof sleep is terrible for your health, mental ability, and mood. in fact it’s a predictorfor depression, and has been linked to things like weight gain, as your hunger-arousingand -suppressing hormones get out of whack. sleep deprivation also causes immune systemsuppression, and slowed reaction time which

is why you should not drive sleepy. of course, a bad night’s sleep here andthere is part of life, but there are a host of bona fide sleep disorders out there thatcan really make life pretty terrible, or in mike birbiglia’s case, land you in the emergencyroom. we’ve got insomnia, which is persistentproblems of falling or staying asleep. and kind of its opposite, narcolepsy, whose suffererssometimes experience brief, uncontrollable attacks of overwhelming sleepiness, called“sleep attacks.” this, as you can imagine, can get in the way of all sorts of thingsthat you might enjoy doing, like driving, eating, pole-vaulting.

narcolepsy may have several different causes,including a deficiency in the neurotransmitter hypocretin, which helps keep you awake. butin more rare cases, brain trauma, infection, and disease may contribute to it as well. so, that’s rare, but you probably know someonewith sleep apnea, the disorder that causes sleepers to temporarily stop breathing, untiltheir decreased oxygen levels wake them up. birbiglia, meanwhile, turned out to have arem sleep behavior disorder, which we don’t fully understand yet, but appears to be associatedwith a dopamine deficiency. then we’ve got night terrors, which areas terrible as they sound... spurring increased heart and breathing rates, screaming, andthrashing that’s seldom remembered upon

waking. night terrors are most common in childrenunder seven, and may be spurred by stress, fatigue, sleep deprivation, and sleeping inunfamiliar surroundings. much like sleepwalking and sleeptalking, night terrors occur duringthe nrem-3 stage of sleep, and are not the same as nightmares, which occur, like mostdreaming, during rem sleep. but oh, in rem sleep, what dreams may come...there you are, running naked as your teeth fall out, being chased down the beach by amatt damon centaur. you wake up, feel around your mouth thinking what? what? what?! what?! welcome to your dreams, those vivid, emotionalimages racing through your sleeping brain, often providing a backdrop so bizarre thatit may seem like david lynch, terry gilliam,

and tim burton are trying to out-weird eachother in a film festival. a really, really long festival, considering the average personspends about six years of their lives dreaming. so yeah, sometimes you have really crazy dreams.but mostly, your average dream usually just sort of unpacks and reshuffles what you didthat day. for example last night i dreamt about tumblr, cause i spent a lot of timeon tumblr yesterday. if you played tetris all afternoon, you mightdream of blocks falling from the sky. if something traumatic happened to you, your brain mightprovide you with a nightmare to help extinguish your daytime fears - thanks, brain! then again...you might be unable to stop dreamingabout the trauma, which we’ll look at in

the future when we discuss post-traumaticstress disorder. our two-track minds of course allow us toregister more stimuli than we outwardly acknowledge during the day, and in that way, the soundsof car alarms or stinky dog farts that you might not even have noticed may get incorporatedinto your dream, too. and that’s all interesting and weird andsometimes a little gross, but what’s the real purpose of dreaming? whyyy do we do this?well, as you might have guessed, there’s more than one idea out there…the study of dreams is is a mix of neuroscience and psychology known as oneirology. oneirosis the greek for dream, and if you’re a neil gaiman fan you may recognize it as oneof the sandman’s many names. the one that

comes with a toga and orpheus’s head. but sandman aside, if you want to talk dreams,we might want to start with our old friend freud.in his landmark 1900 book the interpretation of dreams, freud proposed that our dreamsoffer us wish-fulfillment. he thought a dream’s manifest content, thestuff you remember in the morning, was a sort of censored and symbolic version of whateverinner conflict was really going on in that dream’s unconscious, or latent, content. not surprisingly, the wish-fulfillment theorylacks scientific chops and has for the most part fallen out of favor -- because, really,you can interpret a dream any way you want.

like, sometimes a cigar is just a cigar. luckily we have some other theories to consider.the information processing theory proposes that our dreams help us sort out and processthe day’s events and fix them into our memories. this may be particularly important when itcomes to learning and remembering new information, and some studies show that people recall newtasks better after a good rem sleep full of dreams.but if brainwave readings show us anything, it’s that there’s a lot going on in yourbrain when you dream, and the physiological function theory suggests that dreaming maypromote neural development and preserve neural pathways by providing the brain with stimulation.when our brains are stimulated, they expand

their connections more. so, babies, for example,spend much of their sleep time dreaming, perhaps in part to help their brain circuitry developmore quickly. this is similar to the idea that dreams arepart of our cognitive development. by this model, dreams draw on our knowledge and understandingof the world, mimicking reality, and engaging those same brain networks that light up whenwe daydream. and finally, there are theories that focuson the way rem sleep triggers neural activity, and the idea that dreams are just sort ofaccidental side-effects, the brain’s attempt to weave a story out of a bunch of randomsights, emotions, and memories -- which is how in dreamland you might actually marrythat matt damon centaur and give birth to

a baby with banana fingers and a raccoon tail. for now scientists continue to debate thefunction of dreams, but one thing we know for sure is that rem sleep is vital, bothbiologically and psychologically. but, hey, you think your dreams are nut-bar?next week, we’re looking at other altered states of consciousness, where you’ll learnwhat your brain really looks like on drugs, and whether you can actually hypnotize someoneto do your evil bidding… or just act like a chicken. for now, if you’ve stayed awake during thisepisode, you learned about the four stages of sleep -- nrem 1, 2, 3 and rem itself -- aswell as some major theories for the psychological

purpose of dreaming, including informationprocessing, physiological function, cognitive development, and neural activity models.thanks for watching, especially to all of our subbable subscribers, who make this wholechannel possible. if you’d like to sponsor an episode of crash course, get a speciallaptop decal, or even be animated into an upcoming episode, just go to subbable.com/crashcourse.this episode was written by kathleen yale, edited by blake de pastino, and our consultantis dr. ranjit bhagwat. our director and editor is nicholas jenkins, the script supervisoris michael aranda, who’s also our sound designer, and the graphics team is thoughtcafã©.