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Dreaming is one of the weirdest things we do & in this SciShow infusion Hank talks about how science is helping us understand why we dream, what our brains are up to when they're doing it, and why dreaming may be critically important to the function of our waking brain. He also touches on the fascinating subject of lucid dreaming. Try to stay awake!

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Lucid Dreaming


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Dreaming's gotta be one of the weirdest things we do. I mean, I don't wanna diminish all the other strange crap our bodies are capable of, 'cause a lot of it's pretty cracked out. But dreams are a special kind of crazy, like no matter how many dreams you've had in your life, every once in a while you wake up like, "What the hell was that?" But as with everything else, science is helping us understand why we dream, what our brains are up to when they're doing it, and why dreaming may be critically important to the functioning of our waking brain. So try to stay awake or this one, 'cause it's pretty cool.


People have been trying to understand dreams since there were people. But the person we most associate with the science of dreaming is probably Sigmund Freud. In 1899, he wrote The Interpretation Of Dreams, where he suggested that dreams were largely symbolic and allowed us to sort through the repressed wishes that piled up in our unconscious mind.

And most of those wishes, you might have noticed, involve kinda weird sex stuff. Freud was, you know, Freud. It wasn't until the 1950s, when scientists first had tools that allowed them to read the electrical activity of the brain that we began to understand what a dreaming brain was really up to.

Two researchers at the University of Chicago, Eugene Aserinsky and Nathaniel Kleitman, pioneered this research by hooking people up to the new EEG machine and monitoring their brain activity while they slept. What they thought they'd find was that the sleeping brain was a resting brain but what they discovered was exactly the opposite.

They found that brain activity actually fluctuates in a predictable pattern over a period of about 90 minutes. This cycle takes sleepers from an initial period of drifting off, gradually into a really deep sleep with slower brain activity, back into almost wake. The state of sleep where the sleepers were almost awake again was the most interesting. Brain activity in this phase was almost identical to when people were awake. But even more weird, during this stage the subjects became functionally paralyzed. The only parts of their bodies that moved were their eyes, which darted back and forth under their eyelids.

So you know this part already. Aserinsky and Kleitman called this period REM sleep, after the rapid eye movement that characterized it. They also called it paradoxical sleep because the subjects seemed to be awake, according to their brain activity, even though they were basically dead to the world. They probably figured that these names were better than "sexually aroused sleep," which is another common feature of this stage. But another thing that scientists found out was that if REM sleepers were awakened, they reported having really vivid dreams that were often emotionally intense. It wasn't the only stage of sleep in which the subjects dreamed, but it was the time that they reported having the most lifelike dreams.

It turns out that every 90 minutes or so, during the final stage of the sleep cycle, the brain phases into the REM sleep and our brains start creating crazy narratives that might last between 20 and 30 minutes. This is when you have those crazy, really vibrant dreams that you can almost confuse with reality. So, why so busy, sleeping brain? And what's so important about dreaming that you have to paralyze my entire body in order to have realistic dreams?

Well, there are probably several answers, but one of them is that during the periods of dreaming, our brains are making important connections between real-life experience that will help us in our waking lives. These days, researchers are finding that Freud was wrong about dreams in at least one important way: we don't dream much about our hidden desires. We mostly dream about what we did that day.

When we're sleeping, our brains are sorting through what happened while we were awake, deciding which new experiences were important enough to remember and which ones should get tossed, and searching for links between seemingly unrelated events that might help us be a more successful human tomorrow.

And it's actually really important that we do this while we're asleep because our conscious waking brains are generally too controlling to allow this kind of creative problem solving. And this dream-time activity helps our waking brains be better at things that require making connections and thinking outside the box.

Dreams have actually been responsible for some really important inventions and discoveries in history. For instance, Dmitri Mendeleev came up with the system for the structure of the periodic table of elements in a dream after months of grueling conscious thought was getting him nowhere. And research shows that our brains are much better at solving puzzles if they're allowed to take a nap in the middle of doing one.

In a study in 2004, for instance, subjects were asked to search for links between two sets of numbers. The subjects who napped solved the puzzle 60% of the time, whereas only 25% of non-nappers were able to do it. In another study where people were asked to find connections between seemingly unrelated words, those who lapsed into REM sleep between sessions solved 40% more puzzles than those who didn't.

So, dreams are all about making associations and finding patterns that our waking brains have a hard time detecting. But it seems to work slightly differently in non-REM sleep than in REM sleep.

During non-REM sleep, you dream, but the dreams aren't necessarily vivid and they're often about something you've been doing or thinking about a lot. During these stages, people often report dreaming about kind of boring stuff. Like, if you spend a lot of time in the car during the day, that night, you might dream about driving down a long street, stopping at a series of stoplights. This might seem lame, actually, it's pretty lame, but it's kind of useful to the brain in its own way. It's telling itself things that it already knows, like when you're driving a car, you're supposed to stop at stoplights. So in non-REM sleep it's basically reinforcing existing connections.

But in REM sleep, we get to test out that reinforced knowledge in a context that's virtually indistinguishable from real life. It's like our brain running simulations. So, say you've been driving to your grandparents' house in Boca Raton all day. In the non-REM sleep, you spend a good 20 minutes doing boring stuff like practicing stopping at traffic lights. During REM sleep, your brain might have you trying to steer a steamroller through Manhattan from the backseat.

REM dreams can be very lifelike and very stressful, but that's a part of it. A vivid REM dream is an opportunity to safely let us try something difficult. 'Cause our brains aren't here to make friends; our brains are here to win. The evolutionary purpose of dreaming, like the evolutionary purpose of virtually everything else we do, is to make us more successful animals tomorrow than we were yesterday. In REM sleep, the brain is actually trying to experience the future in order to test possibilities.

So, maybe you're making out with your 7th grade algebra teacher on Jay-Z's yacht while wearing a banana suit. What of it? Does it mean you subconsciously wanna make out with your 7th grade algebra teacher? Maybe, but not necessarily. Does the banana suit have something to do with penises? I don't know; I'm not Freud! The thing is, during REM sleep, you could try that experience with no consequences whatsoever.

Another benefit of REM sleep is that it helps us process emotions that our dunderheaded waking brains aren't really equipped to handle. Although the content of our dreams may be wacky, the emotions attached to them are completely real. Remember, your dreaming brain is charged with working on real-life problems, so if you feel really angry at your boyfriend in a dream, chances are you're probably pretty pissed at him or maybe someone else you're close to in real life.

The stories our dreams create are essentially attempts to give our emotions a narrative that can kind of suck the poison out of them and give them a form our brain can deal with better. In fact, there are people who can't experience REM sleep and they often experience other psychiatric disorders.

So, dreams help regulate the traffic between our experiences, our emotions, and our memories, so we can dial down the crazy. And hey, if the outcome makes your rational brain a little bit uncomfortable, well, that's just how the sausage is made, folks.

Now, since I'm on the topic of weird dreams and REM sleep, a lot of you have said that you'd like to know more about what's called lucid dreaming. This is where you become aware of the fact that you're dreaming and can actually direct the narrative of the dream. Since REM sleep is a simulation in the brain, lucid dreaming is basically a simulation that lets a portion of your conscious brain in on the action. Most of us can probably recall at least one lucid dream and about 1 in 10 of us have them regularly. Some lucid dreamers can even communicate with researchers studying them through gestures like eye movements and hand squeezes.

What ultimately separates lucid dreams from regular old REM sleep may lie in the physiology of the brain. During non-REM sleep, the cerebral cortex, that's your gray matter, loses the ability to associate with other parts of the brain. This is probably why those dreams are more boring and less complex, but once a dreamer reaches REM sleep, the cortex becomes active again and begins talking to other areas of the brain except for this one little part of the cortex called the dorsolateral prefrontal cortex; that doesn't reactivate.

This is the region right about at your left temple that's responsible for, among other things, applying memories to other situations, like planning stuff and predicting outcomes. This helps explain why REM sleep dreams are often so weird; your brain literally can't tell what's going to happen next. But during lucid dreaming, the dorsolateral prefrontal cortex actually does wake up, which is probably why we regain a sense of self-awareness and can plot out stories for ourselves.

Some people claim that lucid dreaming can help with reoccurring nightmares or even help cure depression and anxiety. The jury, though, is out on that, but dreaming itself, all kinds of dreaming, is definitely useful and even imperative to the function of the brain. So, if you're still awake, go take a nap or something. 'Cause it's good for you.

Thank you for watching this episode of SciShow; I hope you learned something. If you want to learn more, you can go to and subscribe. If you have any questions or ideas or comments for us, you can leave them for us on Facebook or on Twitter or, of course, in the comments below. Goodbye.