1Hey, it's Esther.
2My cat Olive loves to nap.
3Her favorite spot is anywhere with warm sunshine.
4But sometimes she'll come into my office while I'm working,
5stretch out on her back, and fall into a deep sleep.
6She is out.
7If I accidentally make a loud noise, she stays asleep,
8but her paws wave around.
9It's almost like she's saying, "Hey, quiet down!"
10Someone named Peyton is curious about what happens when animals sleep.
11Let's give Peyton a call now.
12Hi, Esther.
13Hi, Peyton.
14I have a question for you.
15Do animals dream?
16That's a great question.
17We know that people dream because we can share stories about our dreams.
18But unfortunately, we can't chat like that with animals, at least not yet.
19There are things I've seen animals do when they sleep that make me wonder if they dream.
20Like when Olive waves her paws.
21Or check out this dog.
22He's asleep, but see how his feet twitch?
23And now it looks like he's running.
24Could that be a sign that he's dreaming about running?
25Like a dream where he's chasing after a ball and his body is acting out what's happening in the dream?
26And watch this sleeping cat.
27She hissed so loud that it woke her up!
28Hissing is a cat's way of saying, "Stay away!"
29So maybe she dreamed about something scary, like a vacuum cleaner.
30Olive hates those.
31Maybe you've seen pets do similar things while they sleep
32and wondered if that was a sign that they were dreaming.
33And you can probably think of lots of other animals that sleep too.
34How could you tell if those animals are dreaming?
35Maybe you have some ideas.
36This is a tricky question,
37especially since animals sleep in such different ways.
38How do you tell if a bat is dreaming?
39Or a turtle?
40Or a whale?
41Well, one idea scientists have is to observe what happens when animals sleep
42and compare that to what happens when people sleep.
43Since we know for sure that people dream,
44scientists are still figuring out exactly how to tell when a person is dreaming.
45But their best guess is that dreaming looks like this.
46Looks like a bunch of squigglies, right?
47But those squigglies show what's going on inside a person's brain.
48The lines come from an EEG,
49which is a machine that measures brain activity.
50It's kind of like how a heart monitor shows your heartbeat as a zigzag line.
51This person is wearing a cap with sensors that connect to the EEG.
52When there's activity in the person's brain, like their brain is doing something,
53it shows up on the EEG as wavy lines.
54Sometimes, when you sleep,
55the activity in your brain looks like big, spread-out waves.
56But other times, it's these short, fast waves all packaged together.
57They look a lot like the waves your brain makes when you're awake,
58when you're thinking and learning.
59So why is there fast activity in parts of your brain when you're just lying there asleep?
60Scientists think it's because you're dreaming.
61If dreams happen when there's a lot of fast activity in people's brains,
62we can check if something similar happens when other animals sleep.
63Like this cat.
64She's wearing EEG sensors like you saw before,
65so scientists can see what her brain activity looks like.
66Scientists found that when dogs and cats sleep,
67they also have moments where their brains have lots of fast activity,
68a lot like we do.
69Which means dogs and cats might dream like we do too.
70So Olive might really be dreaming when her paws twitch.
71Scientists have studied how lots of other animals sleep as well.
72But sometimes it's difficult to study all animals' brains.
73The animal might be really big or really small
74or live somewhere hard to reach.
75So scientists look for other signs that could show a lot of activity happening in a sleeping animal's brain.
76For instance, this is a jumping spider.
77It's hard to see here, but...
78when it sleeps, parts of its eyes will make sudden quick movements.
79Sounds kind of weird, right?
80But your body does something similar when you sleep.
81Watch this person's eyes.
82Do you notice how they're moving?
83Scientists call that rapid eye movement, or REM for short.
84REM happens during some of those times when there's lots of fast activity in your brain,
85times when dreaming is likely to happen.
86So if people wiggle their eyes when they dream,
87maybe jumping spiders wiggle their eyes when they dream too.
88Can you imagine what a spider's dreams might look like?
89Different animals experience the world in such different ways,
90and it makes sense their dreams would be just as different.
91I mean, think about what life would be like if you were a dog.
92You'd probably use your sense of smell to explore.
93And maybe you dream in smells too.
94So in summary, it's difficult to know if animals dream.
95But one way scientists are figuring this out is by comparing other animals with people.
96When people sleep, sometimes there's lots of fast activity in parts of our brains.
97And that's when dreaming likely happens.
98When some animals sleep,
99there are signs that their brains also get very active, a lot like ours do.
100So maybe they dream like we do too.
101That means cats, dogs, and even jumping spiders might dream,
102as well as chimps, mice, pigeons,
103bearded dragons, octopuses, and many others.
104But animal dreams would be very different from ours since they experience the world in such different ways.
105So while we can't say yes for sure,
106there's evidence that some animals do dream.
107And maybe someday, you'll find more clues that help us answer if animals dream.
108That's all for this week's question.
109Thanks, Peyton, for asking it!