You're working on one of the most pressing problems in chemistry: the structure of Benzene.

Benzene is a  smelly and highly flammable hydrocarbon molecule. All hydrocarbons are

made of… you guessed it, hydrogen and carbon. But in benzene the ratio of these elements

is a little weird. Instead of having more hydrogen atoms than

carbon atoms, like most hydrocarbons, benzene has the same number of hydrogen and carbon

atoms: 6 and 6.  What strange molecular structure could let

these atoms fit together? Frustrated, you turn your chair towards the

warm fire and take a nap.  As you sleep, visions of atoms and molecules dance in your

mind's eye. They turn into a series of snakes. Then, suddenly, one of the snakes coils around

and bites its tail like the ancient symbol of the ouroboros.

You've solved the chemical structure of benzene… in a dream! Precisely as German

chemist August Kekulé did in 1862, completely changing the future of organic chemistry in

the process, a contribution to science that earned him a statue that people love to dress

up.  And it all happened while he was asleep.

Thanks to… a dream? It makes you wonder: Why DO we dream? 

Hi Smart People, Joe here. August Kekule's dream discovery of benzene's

molecular shape is one of history's most famous dreams. 

But for most of us, dreaming is about more than making chemistry discoveries. Humans

have been trying to figure out why we dream for thousands of years, probably as far back

as we've been asking questions. And since it's an experience we only have while we're

asleep, it's a particularly tough question to answer.

Going back to the Greek philosopher Plato and the Confucian scholar Zhu Xi, great minds

have speculated about the function and meaning of dreams.  But it's only been in the last

few decades that scientific experiments have started to show us what benefits our nocturnal

narratives could have. That's right: benefits, with an S. Scientists

think dreams might have many functions that influence our success, our smarts and even

our survival. We each spend about two hours dreaming every

night. Over an 80-year lifetime, that's almost 60,000 hours, or the same as ten years

of waking life! Dreaming clearly must have some benefit – otherwise

we wouldn't spend so much darn time doin' it.

And everyone dreams…. Even if we don't always remember them. You are more likely

to remember your strangest ones… like I had this one dream where Tom Hiddleston and

I were rowing a boat across the ocean, and then we got hit by a storm, and we were eating

sandwiches. That was weird. (that really happened) Almost half of us remember at least one dream

a week, and women are more likely to remember their dreams daily compared to men. There

are a number of phases the brain goes through during sleep; these phases are repeated in

cycles throughout the night. In the first phase we transition from wakefulness into

sleep, as you begin to relax and your breathing slows. As your body temperature drops and

your breathing slows down even more, you enter light sleep. After that, you enter the deep

sleep phase characterized by a particular pattern in your brain called delta waves.

After that, you start the REM or “rapid eye movement” sleep stage. Your breathing

gets faster, and your eyes move all over. During REM is when dreaming happens. And throughout

this phase, your brain is very active -- almost as active as when you are awake.

Almost all other animals-- whales, wombats, wildebeest…. Sleep. And many also experience

REM sleep. So scientists think that many of these animals also dream -- including your

cat or dog.  Probably about chasing that delicious, juicy,

red ball. The way we think about dreams has changed

a lot throughout history. In most cultures around the world, dreaming has held spiritual

significance. There are even dream interpretations in the Bible.

But there was nowhere where decoding dreams was more popular than in ancient Egypt. The

Egyptians created volumes of books full of common dreams and their supposed meanings.

Professional dream interpreters used these books to help people figure out what their

dreams meant. Dreamer: I had a dream my leg came off!

Interpreter: Oooof, that means dead  people are judging you.

Dreamer: Yikes! — 

Dreamer: I dreamed I died violently! Interpreter: Oh that's a great!

Dreamer: Really? Interpreter: Really! It means you'll live

a long life. Dreamer: Okay?

—  Dreamer (beaming): I had a dream I poured

a jug of my pee into the Nile. Interpreter (confused): Really?

Dreamer: Really! Interpreter: Well actually that's a great

omen too! It means your harvest is going to be bountiful.

Oh right… obviously. The belief that dreams held hidden messages

to be interpreted or decoded remained the dominant way to look at dreams through the

first part of the 20th century. In 1900, Sigmund Freud published the influential

book “Interpretation of Dreams.”  In it, he claimed that dream interpretation could

be used to understand unconscious desires.  It all started when he had a dream, a dream

so famous it has a name… and a Wikipedia page. 

It's called Irma's Injection.  “A large hall - numerous guests, whom we

were receiving. - Among them was Irma.” It was about a former patient of Freud's

that he felt he wasn't able to completely heal because she refused his treatment. 

“I at once took her to one side, as though to answer her letter and to reproach her for

not having accepted my 'solution' yet.” This dream sparked Freud's theory that our

wishes that aren't fulfilled while we're awake are expressed in our dreams. Because

some of those wishes might be kinda embarrassing, Freud thought our minds deliberately confused

the dreams to hide their true meaning. Carl Jung expanded Freud's theories. Jung

considered archetypal symbols that often appeared in dreams, like a wise old sage, or a trickster,

to be universal among humans. Jung thought that dreams were interpretable… if we could

crack the code of these universal symbols, the “language” of dreams. According to

Jung, dreams had two functions: they compensated for things that the dreamer ignored or repressed,

and they looked forward to give the dreamer hints about what might happen in the future.

Lots of people still look for meaning in their dreams, especially to do with the future.

In one study, people were more likely to say having a dream about a plane crash the day

before a flight would make them cancel their trip than if they were given a government

warning about a “high risk of a terrorist attack.

But modern science has moved away from Freud and Jung and viewing dreams as buried messages

to decode or interpret. Today researchers are asking what functions and benefits our

brains themselves might get from dreaming. At first, scientists believed that the strange

mish-mash of pictures, stories, and events we experience while dreaming were just side

effects of basic biological processes in our brains, a sort of neurological noise that

we experience as we sleep. Scientists thought that other parts of the

brain tried to make sense of the noise by threading this random slideshow into a story…

often a very weird story. This is called the Activation-Synthesis Theory of dreaming.

But experiments showed that dreams are not actually random. Some things are more likely

to appear in our dreams than others. And scientists began to wonder: Maybe dreams aren't random

noise… maybe our brains NEED to dream to be healthy. .

What we dream about often has to do with what we do while we're awake…especially if

we're learning something new.   In one study, about a third of participants

who played Alpine Racer II, an arcade downhill skiing simulator, had dreams about the game.

Consider this: The things that happen to you every day only happen once. In our short-term

memory, these experiences are fragile, and can easily disappear. Our daily experiences

might only make it into our long-term memory if they're RE-played several times - you

guessed it - in our dreams. Patterns of brain activity just after dreaming look a lot like

when our brains store and retrieve episodic memories – memories of things that actually

happen to us. So, dreams may be a sort of memory replay of our experiences … with

an extra layer of weird on top just to make it fun I guess.

In one study to test this, scientists asked people to play 7 hours of Tetris across 3

days. Hang on, I have a question… Where do I go to sign up for these studies? Anyone? 

I'm busy right now. I'm doing some science! Woo! Serious brain science here.

Anyway. After some serious Tetris time, participants reported seeing images of tetraminos when

falling asleep. They seemed to be replaying the game to store their new skills in long-term

memory. It's not all fun and games, though. Dreams

can turn into nightmares. There's no universally accepted definition of what a “nightmare”

is, but they're commonly considered a “distressing or terrifying dream,” one that goes so far

as to wake you up.  About one in 40 dreams is a nightmare. So why do our brains replay

our worst fears and memories? The Threat-Simulation Theory suggests that

dreams let us “practice” dangerous events and situations. That's why some people relive

traumatic experiences in dreams. The brain is trying to condition us to survive threatening

experiences by “practicing” in a safe environment -- inside our sleeping brain.

Back when life-threatening situations were a part of our species' everyday life, simulating

threats could've helped us survive. But in the modern world, reliving awful situations

in chronic nightmares can be debilitating. But we also practice social situations in

dreaming. That's the Social Simulation Theory of dreams. Scientists noticed our dreams are

heavy on social situations: a fight with a close friend, a date with a crush, a clash

with a coworker, or not wearing pants to school. Since being social is so important to our

species, practicing these situations would have been an evolutionary advantage.

The strange experience of dreaming can be used for problem solving too.  

Novelist John Steinbeck once said: "It is a common experience that a problem difficult

at night is resolved in the morning after the committee of sleep has worked on it.”

When college students were given a homework problem to focus on each night before bed,

a quarter dreamed the answer within a week. Because dreams aren't limited by...um…

logic… or physics … they're a great place to problem solve and come up with creative

—and sometimes weird—solutions. Which is especially helpful when solutions to problems

need a very different approach compared to conventional wisdom. And this may be why we

owe many pieces of great art to dreams: The Beatles' iconic song Yesterday, Salvador

Dali's melting clocks, Mary Shelley's novel Frankenstein, and countless others.

So, can you dream your way to a Nobel Prize? Or a Grammy? Well… maybe. Scientists are

experimenting with “Dream Incubation” as a way to prime the brain before sleep to

be more creative. So… because dreaming is so common, and because

we spend so much of our lives doing it, it's almost certainly useful, for one or many reasons.

But why did dreaming evolve to begin with? Maybe thanks to the… rotation of our planet?

That's right. Scientists think the origin of dreaming just might have to do with the

sheer amount of time that humans – and all animals – spend in the dark.

Our ability to use our peepers and see the world around us is an extremely important

evolutionary advantage. And because it's so important, the part of the brain responsible

for sight, called the visual cortex, takes up a big chunk of our brains.

But there's the thing. Our brains can also be rewired pretty easily. If you were blindfolded,

your brain would begin to change within an hour of not using your sight. The neurons

of the visual cortex start being taken over for other tasks.

The lengthy darkness of nighttime, would have meant that the visual cortex of our human

ancestors was at a high risk of being taken over by other functions while we slept. If

we didn't use it, we could lose it. Dreams, and their highly visual nature, may have evolved

in mammals to keep these vulnerable brain areas active at night… And keep the brain

from rewiring itself in unfortunate ways. So… which is it? Is it problem-solving,

or practicing, or seeing, or is it problem solving or not about seeing, or a bit about

practicing and a pinch of problems solving? Scientists don't know if one or many of

these ideas will prove to be correct, and so research continues. Ah, science.  Always

figuring stuff out. But never quite figuring stuff out all the way.

It's even possible that dreams may have evolved for one function, but stayed around

so long because dreaming ended up helping us in a bunch of other different ways.  Trying

to peer into the workings of the sleeping brain is one of the most challenging problems

in psychology and neuroscience, but we're building a fuller and fuller picture of the

science of dreaming, one dream …at a time. You wouldn't believe the dream I just had.