[MUSIC]

For many of us, the worst moment of every day goes something like this…

[ALARM CLOCK NOISE]

That noise marks our daily return from the

mysterious world that we call sleep. We spend a third of our lives asleep, yet, other than

the odd snapshot of a dream here and there, most of us have no idea what happens after

we close our eyes.

Luckily we’re in good company, because there’s also a lot scientists don’t know about sleep, too.

For a long time, it was just something that happened, everyone assumed that our brains

were hitting the reset button and just turning off for a while. But in the past few decades

it’s become clear that sleep might be the single most important behavior that humans

and other animals experience.

It might seem like we don’t do much while we're sleep, but neuroscience tells a different

story. Human sleep patterns are controlled by two competing networks of chemical and electrical signals in the brain.

During our waking hours, neurotransmitters released deep within our brain keep our cerebral

cortex alert and primed for consciousness. But throughout the day, as our neurons break

down ATP for energy, the byproduct adenosine builds up and activates sleep control neurons

near the hypothalamus.

A special region in the center of our brain acts as our master biological clock.

Light sensitive cells in our retinas feed signals deep into that brain region, training neurons

to sync up with Earth’s 24 hour cycle of day and night. These circadian rhythms are

the control switch that tells us when to feel sleepy or awake.

As the world goes dark, this master switch tells our pineal gland to increase levels

of the hormone melatonin in the bloodstream, sort of like a chemical lullaby. Feelings

of fatigue set in, body temperature lowers slightly, that heat loss is actually why many

of us like to fall asleep with our feet sticking out of the covers, true story! Together all

this neurochemistry sends one clear message to our bodies: when it’s dark, it’s time

to go to bed.

Unfortunately, in modern times, darkness is increasingly rare. In the United States, 99

percent of people live in areas that meet standards for light pollution, and we’ve

got one person to thank for that: Thomas Alva Edison.

Edison thought sleep was lazy, unhealthy, or inefficient, even though he took several

naps a day. But despite that hypocrisy his work more/sleep less view changed our world

forever. Illuminating the night became a sign of economic progress, and humankind was no

longer at the mercy of nature’s clock. Or so we thought.

Artificial light can have serious effects on our sleep cycle. When we’re exposed to

bright light at night, our brain doesn’t know better than to think the sun is shining.

This can be very confusing, preventing the release of melatonin and the onset of sleep.

Depression, heart disease, diabetes, and cancer have all been linked to chronic overexposure

to artificial light.

Until just a couple hundred years ago, it was common for people to fall asleep right

after the sun went down, snooze for a while, wake up around midnight, where they would

read or study or do other stuff, then go back to sleep until morning.

Modern experiments have suggested that if people are kept away from artificial light,

their bodies will return to this pattern of first and second sleep, yet most of us insist

on sleeping the whole night through. What’s worse, our circadian rhythms are so tuned

to day and night that if we stay up past our usual bedtime, we don’t wake up later, we

just tend to sleep less.

As a result, we’re massively sleep-deprived. Most adults average just six and a half hours

a night. Teenagers average just five hours on school nights, which is half of what they

need. To fight this chronic exhaustion, we turn to stimulants like caffeine to help our

brains ignore that buildup of adenosine, and then to fight the stimulants, many people

rely on alcohol, which just sedates us, it doesn’t even help with real, restful sleep.

This vicious cycle is worth literally billions of dollars a year. It’s kinda messed up.

I still love you though, coffee.

So what is sleep for? In short, we’re not really sure, but we know it’s essential

to life. Animals deprived of sleep for a long enough time will have seizures, and can literally

die from exhaustion, plus a whopping 15% of our genes are linked to circadian rhythms.

Still, there’s no consensus on exactly why our bodies need sleep.

We’re definitely less active at night, but considering we only burn about 100 fewer calories

while sleeping, it’s not a very good energy-saving strategy overall. We definitely do a lot of

cellular repair, protein synthesis, and general biological upkeep while we’re in dreamland,

but it’s not like we don’t do that stuff when we’re awake too.

Another theory says that our bodies use time asleep to flush out all the neurogarbage,

removing waste products that build up in our neurons and brain cells. And, decision-making

regions of our brain like the prefrontal cortex, well they don’t get any downtime while we’re

awake, like even if you’re totally relaxed and you think your mind is clear, your prefrontal

cortex is still prefrontal cortexing. Just try and think about nothing. Go ahead. See?

You’re thinking about not thinking. Sleep seems to be the only time for this region

to power down and get a break.

The greatest benefit of sleep may lie in processing information and consolidating memories from

throughout the day, letting the brain do all the rewiring that is necessary for thinkin’

better. Sleep deprived people do worse when learning new tasks and they're less able to

process new information, whereas a good night’s rest appears to make us more creative so we

can come up with solutions to new problems that we haven’t seen before.

Perhaps the biggest mystery is how sleep evolved in the first place. Snoozin’ animals are

easy targets for predators, so you’d think evolution would have come up with something

better. But it hasn’t. There’s no way to get around the need for sleep.

Some animals have come up with interesting ways to deal with the inconvenience of sleeping,

though. Dolphins obviously can’t nod off without drowning, so they only sleep with

one half of their brain at a time, swimming along using the half of their body that’s

still awake. Before baby dolphins learn that trick, they take adorable little dolphin naps

while their parents keep them afloat.

Sleep or similar patterns of rest are seen so universally throughout the animal kingdom

that they must have an ancient origin, and one clue comes from a tiny, ocean-dwelling worm.

Every night, these worms swarm near the surface of the ocean to feed, and every day they sink

down deep to avoid light and predators. The worms have special daylight-sensing cells

on their back, just like the ones in our eyes. When it’s dark, those cells trigger the

production of melatonin, just like in our brains. As the melatonin builds up, tiny hairs

on their bodies stop beating and the worms begin to sink, just in time for the sun to

come up. As the melatonin disappears throughout the day, the hairs begin beating again and

they swim back up to the surface to do it all over again.

Sleep might have evolved 700 million years ago, the last time we shared a common ancestor

with that tiny worm. It's pretty important, so maybe we should all make a little more

time for it.

If you want to learn more about the science of sleep, one book that really helped me is

“Dreamland: Adventures in the Strange Science of Sleep” by David Randall. And also, be

sure to check out this half-hour playlist from our friends at The Good Stuff that digs

even deeper into what are brains are doing while we’re asleep, plus Craig goes to a

sleep lab to find out how to get a better night’s rest. Sleeping on the job, Craig,

real professional. Oh and over at BrainCraft, Vanessa has a video with some scientific tips

on how to beat jet lag. In fact, just make sure you’re subscribed

to The Good Stuff and BrainCraft, they are awesome. Links to all that down in the description.

Stay curious.