Sleep is weird.  We spend about a third of our lives asleep.  Gerbils and lions do it 13 hours a day.  Elephants average only 3.5 hours.  Birds and dolphins only sleep with half their brain at a time, so they can still fly and surface for air.  Obviously it’s important, because animals (humans included) are vulnerable when asleep, and that time could be better spent eating or procreating or finding shelter.  Sleep lets the prefrontal cortex reboot (that’s the decision-making and “thinking” part of the brain), and helps with long-term memory and processing.  There’s a lot to it, but I’m going to focus on how sleep relates to our waking selves in this post.

Until the invention of electric light, humans didn’t sleep through the night.  There was “first sleep”, which was from shortly after dusk until about midnight.  An hour or so later, “second sleep” would last until dawn.  That hour in the middle of the night created a meditative state in people.  Some writers felt they worked best during that time.  Sex was supposedly better then, because both partners were well-rested after what was most likely a long and terrible day.  It may well have been the most relaxing part of humans’ day for most of our existence as a species.

And then we had artificial light.  Light bulbs, televisions, and computer screens can all make the body think it’s supposed to be awake.  It suppresses the release of melatonin, which is the hormone that starts our nightly sleep cycle.  (This is why there’s a trend of taking artificial melatonin at bedtime.  The theory is that it will cancel out the artificial light and make us drift off more easily.)

Experiments have proven that if humans go without artificial light for a few weeks, they start having the segmented sleep of their ancestors.  We’re still wired for it.  Also, light pollution is messing with all the other flora and fauna exposed to it.  Everything from sea turtles to frogs to trees are having their circadian rhythms messed up because of artificial light.  In humans, too much light after dusk has been linked to depression, obesity, heart disease, and a slew of other illnesses, even breast cancer.  (Researchers think that the suppression of melatonin affects estrogen levels.)

We’ve also gotten rid of midday naps, which used to be common throughout the world.  Some modern companies who specialize in generating new inventions have napping rooms in their offices, so that employees’ brains get the mid-sleep inspiration they often need.  There’s a body of research that says our brains process and analyze the problems we’ve been trying to solve while we sleep.  Our sleeping brains rehearse newly-learned skills while we sleep, too.  I’ve read in several books that many actors and musicians will take naps after they’ve been practicing or memorizing pieces, because it helps them retain what they’ve learned.

Circadian rhythms play a part in how well people stay at work, and even athletes.  Pro tip: if you’re ever betting on American professional sports and a West Coast team is playing an East Coast one, always bet on the West Coasters.  Their bodies think it’s earlier in the day, and are more awake as a result.  By the time a Monday night football game finishes, it’s coming on midnight EST and players are exhausted, no matter what time zone they’re currently playing in.

Teenagers, adults, and seniors all have different rhythms.  The teenage brain wants to stay up late and sleep in.  The elderly are in bed early and wake up in the early hours of the morning.  Younger adults are between the two.  Evolution gave us naturally occurring sleeping shifts so that someone was always awake at night to watch for predators.  There’s enough research about teenagers’ different sleep cycle that many high schools start later than they did in the past.  Starting classes at 8:30 or later improves performance, memory, SAT scores, and mental health in the affected teens.

Sleep deprivation causes memory loss, paranoia, aggression, an inability to adapt to new situations, and poor decision-making.  For every 24 hours of being awake, cognitive abilities decrease by 25%.  Our military rarely gets enough sleep, leading to frequent mistakes (such as Pearl Harbor being worse than it should have been, thanks to fatigued sailors), as well as fights with civilians that makes our armed forces disliked by people who encounter sleep-deprived soldiers.  The military knows this.  And yet they still don’t let soldiers sleep enough.  DARPA, the research arm of the Pentagon, wants to find a way for soldiers to stay up and be fully functional for more than 24 hours at a time.  But then, DARPA also wants to surgically implant gills so soldiers can breathe underwater.  DARPA is weird.

Random facts:

Sleeping pills don’t actually help you sleep more than an extra 11 minutes or so, and you fall asleep a mere 12 minutes faster.  Instead they cause mild anterograde amnesia so that you forget how badly you slept.  Cognitive Behavioral Therapy is a far better cure for insomnia.

People can and will sleep on anything and everything, and what’s familiar is considered most comfortable.  People who sleep on concrete get as much rest as someone on a squishy mattress, once they’ve had a few days to get used to the new surface. (And if their body temperature is comfortable; temperature has a lot to do with how well we sleep.)

Our hands and feet get hotter as we’re falling asleep.  That’s why so many of us like to stick out feet out from under the blankets at night.

Pugs, English bulldogs, and other animal breeds with flattened faces are the only creatures besides humans to get sleep apnea.  Neanderthals didn’t get apnea; homo sapiens‘ faces got flatter as a trade-off in the position of our tongues.  We got the ability to speak from that, but it also means we can’t breathe or eat as well as other early hominids.

I’m going to end this post here, with a recommendation to read Dreamland: Adventures in the Strange Science of Sleep by David K. Randall.  Most of this post came from that, but there’s so much I left out.  There’s a good deal about parasomnias (like sleepwalking, or an inability to reach REM sleep), including an interview with the country’s only forensic sleep scientist.  Because yes, it is possible to commit crimes while sleepwalking.  He studies it, and his remarks are fascinating.  There’s also a lot more hard science facts in Randall’s work.  I’m deliberately keeping things light in this blog, to just pique your curiosity and maybe get you to read more.

Also relevant is Grunt: The Curious Science of Humans at War by Mary Roach.  There’s an entire chapter about trying to sleep while on a Navy nuclear submarine that is… disturbing.  Mary Roach is one of my all-time favorite science writers, and her work is hilarious and creepy and informative — frequently all in the same sentence.

Categories: Science


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