[ ♪ Intro ].

Conventional wisdom says we’re supposed to get 8 hours of sleep a night. Fewer of us actually do, with the CDC reporting that a third of American adults snooze for less than 7.

Now, the current consensus from sleep researchers is that we need to sleep for long enough, continuously enough, and deeply enough to receive the proper benefits of sleep. And that’s a long list of benefits… like top cognitive performance, proper storage of memories, or avoiding health problems like high blood pressure and obesity. We need sleep.

But some people try to break their sleep into chunks instead of getting a single — or monophasic — stretch of Zs. Despite the trends, there’s not much scientific evidence to suggest polyphasic sleep is better than monophasic. And some polyphasic sleep patterns are distinctly worse.

We don’t fully understand how sleep works. The leading model for why and when you sleep is called the two-process model. It states that there are two, well, processes going on in your brain that dictate how sleepy you are at any given time.

One, called process C, is a product of your circadian rhythm, or the attunement of your brain to the cycle of day and night. Your biological clock is run out of your brain’s anterior hypothalamus. It ticks along in response to light, and makes you sleepier at night.

The other, called process S, is homeostatic, which is to say it reflects the need for your body to maintain a steady state in all things. We don’t know what exactly regulates process S, but it may have to do with the buildup and clearing out of chemicals like adenosine in your brain. The longer you’re awake, the more sleepy process S makes you.

And the longer you’re asleep, the more likely it is to wake you up. While scientists are still revising the two-process model, those basic parts do seem to explain why we sleep for a long time at night. Process S and process C can change as you get older, and they operate independently from one another.

So it’s possible to separate your sleeping patterns from the pattern of sunrise and sunset. And scientists use this fact to study sleep by placing subjects on an altered schedule. In one oft-cited 1992 study published in the Journal of Sleep Research, 7 participants were placed on a schedule with 10 hours of light and 14 hours of darkness.

Over the course of several weeks, they eventually took to sleeping in two blocks during the dark period, with a few hours awake in between. This, combined with historical knowledge, is sometimes used to suggest that humans naturally adopted a biphasic sleeping pattern in the days before we had electric lights to keep us up. The idea of breaking up sleep into a polyphasic pattern, though, has been taken to some extremes.

The scientist Buckminster Fuller somewhat infamously subscribed to the Dymaxion sleep schedule, which involves 4 30-minute naps evenly spaced throughout a 24-hour period. Some swear by similarly draconian napping schedules, like the Uberman, totaling only a couple hours of sleep per day. While others recommend longer “core” rests at night.

Napping in the afternoon, or taking a siesta, is technically a polyphasic sleep schedule, and it’s followed in many parts of the world. Breaking up your rests could work by affecting process S, basically resetting the make-you-sleepier ticker more often. However, polyphasic sleep isn’t well studied.

When it is, it’s in the context of shift work, like of people providing essential services in hospitals and fire stations. A 2014 study in the journal Chronobiology International argued that 12-hour shifts probably aren’t great for productivity. After 12 hours of work, people may suffer from decreased alertness — especially at night when their circadian rhythm is making them naturally sleepy.

Instead, the researchers proposed shorter schedules, like 6 hours on and 6 hours off, or 4 hours on and 8 hours off. In the experiments they ran, 29 participants were put on a 28-hour schedule with at least 9 hours of time in bed. Half were on a conventional light-dark schedule and half were broken up, with periods of 4.6 hours of rest and 9.3 hours awake.

The two groups didn’t differ in their performance on a test that measured their alertness and reaction times — even though participants on the split schedule sometimes reported feeling less alert. And this led the authors to suggest that shorter work shifts with shorter rest periods could help shift workers. However, it’s important to note the participants still got in a solid one third of their “day” as rest.

Less than that and you enter the realm of sleep deprivation, which comes with a list of symptoms like anxiety, irritability, poor reaction times, and longer-term health risks like high blood pressure and diabetes. Some early sleep research failed to show any ill effects when participants slept for only 4 or 5 hours a day. But now, researchers think those experiments were poorly controlled.

And more recent studies show drop-offs in cognitive function when less than 7 hours are spent in bed. Even worse, you may not know how exhausted you are. Some studies, including one from the journal Sleep in 2003, have found a disconnect between self-reported sleepiness and objective sleepiness as measured by electrical activity in the brain, with EEG.

Sleep-deprived people tended to think they were way better off than their scores on cognitive tests actually indicated. And while it might be okay to break up your sleep a little, researchers have also studied sleep fragmentation — when you wake up too many times during your rest period. For instance, many researchers think that uninterrupted sleep is necessary to store memories properly.

A study published in 2012 in the journal PLoS One found that subjects whose sleep was interrupted during a monophasic rest pattern had an impaired ability to form memories. So while we don’t understand everything yet, it’s clear that we need sleep to be our best selves. And our brains definitely need more than two hours.

You can try to reprogram it if you want to, but it’s at your own risk. Thanks for watching this episode of SciShow! If you want to learn more about some groundbreaking discoveries biologists have made about sleep, check out our list show all about it!

And if you just want to keep getting smarter with us, you can go to youtube.com/scishow and subscribe. [ ♪ Outro ].