Thanks to Babbel, a language learning  app, for supporting this SciShow video.

As a SciShow viewer, you can use our  link to grow your language skills with Babbel for up to 60% off with  a 20-day money-back guarantee. If you have a pet or spend any  time around animals at all, you’ve probably watched them sleep and  wondered what they’re dreaming about.

Maybe your cat is dreaming  that they’re chasing a rat. Maybe your rat’s dreaming about how to get from a tasty pile of food back to their home. But we can do better than just guess.

Scientists have studied the brains  and behavior of all kinds of animals, from birds to octopuses, to  learn about their dreams. And believe it or not, we can often identify  exactly what they’re dreaming about. [♪ INTRO] When it comes to dreams, we  have the most data about humans because people can actually tell scientists  about our thoughts after we’ve slept. But rodents are a close second.

After all, a huge amount of  what we know about the brain comes from rats and mice. And we’re not all that different  from them when it comes to dreams. For both humans and rodents, one of  the main uses of dreaming seems to be replaying the day and making sure  you hold onto its valuable memories.

The difference is that rats do it in fast-forward. Their day runs through their mind at seven times the original speed while they sleep. We know this because of science!

Researchers at the University of Arizona trained rats to run along a  path during their waking hours. While this was happening, they recorded  the output from the rats’ neurons in the part of the brain that helps with decision  making, known as the prefrontal cortex. They looked for patterns in which  cells were active at what moments.

But not just while the rats were running around. They also looked for those  patterns while they slept. As you might expect, the patterns  weren’t there in pre-training slumber.

They first showed up during training. But similar patterns showed up  again afterward during naps! So once they learned the path  they were supposed to walk along, they replayed it in their  mind while they were sleeping.

But that pattern played on easy mode  while the rats were walking the path and ramped up to advanced mode when they slept. By the time they went to sleep,  their prefrontal cortex cells were firing around seven times faster  than they had during the awake trial run. While the speed at which  rodents do this is unusual, many other animals also replay the  things they learned throughout the day.

But they dream about totally different stuff. In the life of a male zebra finch, it’s really  important to learn how to sing from your dad so that you can grow up and find your  own mate to have cute baby birds with. And these aren’t the simple little  chickadee-dee-dee songs that some birds sing.

They’re complex songs with a variety of syllables that combine to form a special  tune unique to that bird. The ladies love a complicated song, because a male who can sing really  complex tunes is probably fit. Which means that instead of being up in the gym, these birds work on their fitness  by practicing ornate melodies.

Even in their sleep. But, once again, we’re not just guessing that they practice their songs in their dreams. We have the data!

There’s a part of the brain called  the robustus archistriatalis that responds to songs in a specific  enough way that trained researchers can read its output like a page of music notes. And at the University of  Chicago, they did just that. They recorded the activity of individual  brain cells in the robustus archistriatalis while birds sang and while they slept.

And they saw the same patterns! But, in contrast to rat dreams, the timing of these sleepy bird  songs was the same as the awake song. You just can’t listen to a  masterpiece like that on 7x speed.

So song birds dream of sweet lullabies. But other animals are contending  with literal nightmares. “Cephalopod” has got to be one of our best words. It’s just really fun to say.

And the animals included in this  category are just as goofy as the word. We’re talking cuttlefish and octopuses. But, as goofy and fun as cephalopods  may be, their dreams get intense.

The way they sleep suggests that  they can relate to our experience of tossing and turning from a bad dream. See, when we do that, it’s because our bodies are physically responding  to a threat in our dreams. And cephalopods do the same thing,  even though we went our separate ways on the evolutionary tree more  than 500 million years ago!

They have a similar kind of REM sleep to us, where they move their eyes and twitch. But they take it to the next level because  they change colors in their sleep too. When they’re awake, they use  this color changing ability to hide from threats and  to communicate with others.

But when they’re asleep, they  sometimes change colors in a way that’s still coordinated but not  relevant to their surroundings. So researchers at the University of  Pennsylvania and Millersville University think it’s a response to  what’s going on in their head, kind of like our physical responses to dreams. And if they’re responding  to threats in their sleep, like a moray eel coming over to eat  them, that sounds like a nightmare to me.

I mean, have you seen those things? They’re terrifying! Now, I know the chances of  you seeing a dreaming octopus are much lower than, say, a dreaming cat.

So let’s get into the science  of Mr. Whiskers’ dreams. Cats, like cephalopods and us, get  a little twitchy while they sleep.

Or, if they’re like my cat, Huckleberry,  they look like they’re riding a bike! He’s so cute! So researchers at the University of Chicago wanted to figure out what makes them tick.

These scientists measured brain waves  in sleeping cats using cat-sized EEGs. And they found that the sleeping cat  brain works a lot like awake cat brains. Sure, we can’t ask the cats  what they were dreaming about, as much as I would like to.

But their brain activity also  looked a lot like ours does when we’re dreaming, so we  have a pretty good idea. And the cats showed the same twitchy legs and rapid eye movements that  we do while we’re dreaming. So far, the most studied hypothesis  for those eye movements is that they’re looking at whatever they’d be directing  their attention to in a dream.

It’s called the scanning  hypothesis because in their dreams, the cats are scanning their environments  for things like danger or a rodent treat. In fact, one study found that the eyes  frequently moved in coordination with their heads during REM sleep. So they’re orienting more of their bodies  than just their eyes while they sleep.

And soon after those eye and head movements, the cats would burst into  action to jump and attack. Ultimately, their bodies and brains were  sending signals like they’re on high alert. But just like the cephalopods, it wasn’t in response to  anything going on around them.

So the scientists figured that’s  probably what a dreaming cat looks like. And that means that at least some of  the time, they might have been dreaming about whatever puts cats on high  alert, like chasing a squirrel. But until someone conducts a study like  they did with rats and compares cat brains while they’re chasing squirrels and while  they’re sleeping, we won’t know for sure.

Obviously, humans, rodents,  birds, cephalopods, and cats live in wildly different environments  with very different stresses. So it’s no surprise that there’s  some variation in our dreams. But the biggest difference seems to be  what’s on our minds when we’re awake.

Usually, we’re dreaming about that. When it comes to replaying our  days and expressing our fears, other animals seem to have  dreams that are a lot like ours. I wonder if they have the one where they  show up to class in their underwear?

On the topic of relatable dreams, do you ever have the one where for  some reason you and everyone around you are communicating in a language  you don’t actually speak? Like, it’s me and my mom  in her kitchen in Florida, but we’re talking to each other in  French and neither of us knows French. Maybe that dream is telling  you it’s time to learn French!

Or maybe you saw a billboard  written in French earlier that day. Either way, if you want to understand  what that billboard says, Babbel can help. Babbel is the #1 language-learning  app in the world, with 14 different languages at your fingertips.

Now, we all want to know more  languages, but it takes a lot of time. So Babbel forms their lessons  to be just 10 minutes at a time, giving more of us the chance to pick  it up little by little every day. After three weeks, you could start speaking  French with your mom in her kitchen.

But for real this time! And conveniently, the 20 days that it  takes to start speaking a new language is the window for Babbel’s money back guarantee. So you won’t lose anything for trying.

And as a SciShow viewer, you can get up to 60% off when you sign up using the link  in the description down below. Choose from different subscriptions,  including a lifetime option, that comes with two free live classes. Thanks to Babbel for  supporting this SciShow video! [♪ OUTRO]