Do Fish Dream?

Do Fish Dream?

[♩INTRO] It’s easy to look at a sleeping dog, legs
twitching as she snoozes, and imagine she’s dreaming of chasing rabbits. And it’s only natural for us humans to wonder
if other animals dream. But dogs’ brains are relatively similar
to ours. What about something way more different from
us? Say, a fish? We don’t yet know exactly why our brains
race through fantastical or scary scenarios at night, but
there are plenty of hypotheses. Dreams may be ways for our brains to process
emotions or memories, or to prepare for new scenarios. Human sleep occurs in a series of cycles. We cycle through a series of phases over the
course of the night, which can take anywhere from 70 to 120 minutes. Most dreams occur during a phase called rapid
eye movement, or REM. As you might imagine, this type of sleep is
characterized by rapid movements of our eyes. It’s possible these eye movements are connected
to our dreams themselves. Researchers have suggested that each flick
of the eye may correlate with a new image being encountered in a dream. But do other animals experience sleep the
way we do? Well, we can’t exactly ask them, but we
sure are curious. And this fascination has led us to study sleep
in fish as far back as 1913. That study set out behavioral criteria for
fish sleep. In zebrafish, that means things like immobility,
a preferred sleeping location, and a reduced respiratory rate. But it wasn’t until a 2019 study that anyone
defined what was happening inside the brains of fish while they sleep. And it took so long because it’s hard to
do! One way to look inside human brains, including
during sleep, is using an instrument called an electroencephalogram,
or EEG. This typically measures activity in a region
of the brain called the neocortex. Fish don’t have a neocortex. However, zebrafish do have something similar, called the dorsal pallium, which the researchers
targeted in this study. They took advantage of the fact that the young
zebrafish are see-through. You can see straight into their brains! They inserted a gene into the fish that caused
their neurons to glow when active. Specifically, it gives off light in response
to calcium. Since calcium levels change as neurons send
their signals, this allowed the researchers to watch brain
activity while the fish slept. Their results showed that like humans, fish
cycle through sleep patterns. The researchers saw two main sleep states: slow bursting sleep and propagating wave sleep. And propagating wave sleep showed a number
of similarities to our own REM phase, though the fish’s
eyes stayed still. The researchers suggested these similar patterns
of sleep activity could have evolved before fish and humans
split, more than 450 million years ago. So, this doesn’t prove that fish can dream, but it suggests that they do go through something similar to our own dream-filled
REM sleep. So, that means fish dreams are a possibility! Thanks to our patron Olan Kenny for asking
this question. Our patrons submit and vote on questions that eventually get made into episodes like
this one! So, if you want to be a part of that process, or just want to help SciShow keep making free
educational videos for everyone you can check out [♩OUTRO]

100 thoughts on “Do Fish Dream?

  1. Yes, yes, yes. Dreaming fish and all that. The real burning question we're all dying to know is do androids dream of electric sheep?

  2. It's reasonable to assume that any creature that sleeps and also has functional memory can 'dream.' This opens the questions: 'what is sleep,' 'what are dreams' and 'what is functional memory'?

  3. dogs brains are similar to ours? is that why they look so stressed out when they're trapped in cars, as if they're thinking "hmm, why didn't my best friend take me with them?"

    i would hate to be leashed or neutered or have a microchip tracking implant or… oh yeah we're talking about fish

  4. Now I gotta see things light up in a fish brain while it sleeps. Did they use a camera or a photomultiplier tube to measure the 'light'?

  5. Sometimes when I close my eyes to sleep, I notice my eyes wandering around even though my they are closed. It's very distracting

  6. Don't gata tell me I had a dream visit with my fish and two others like it. But the other two were looking like spirit fish.

  7. 0:24 I guess that explains why I don't dream much anymore. These days I don't feel much of anything emotionally (just the way I like it) and memories I still have I'd rather forget if I could. No need to prepare for new scenarios either, every day has been pretty much the same as the one before for the past 14 years, no reason to think tomorrow will be any different.

  8. 💡@ p_your:

    Clearly it means my spicy Darthsaber dreams….are just hoarseraddish.

    Also, I love oats as much as you may enjoy my Lightsaber: in a ricey-salmon-bowl covered in—

    Soy…does the sauce stick?


    = Dude, I'm fracking hungdry.🗿

  9. This vid exemplifies the beauty of pure research…..research about a topic someone is just interested in. It isn’t done to find a cure for schizophrenia or cancer. It’s research just because someone said, “I wonder….”

  10. of course, everything with sufficiently complex nervous system 'dreams', that line mostly correlates with vertebrates but also includes few other things eg. cephalopods

  11. As a bird owner, I can attest that birds can have nightmares, which is why I keep them confined to their cage at night as much as I love letting them free range. Even with a nightlight, they'll crash into things in the middle of the night, so I keep them confined for their own safety. So, I would imagine that fish could have nightmares also. What our pets see in their dreams… I don't know, but I would imagine the experience is similar to humans.

  12. Perhaps a better question would be why are we so bloody arrogant that we assume that other animals don't experience what we do?

  13. Hurray for fishes do dream.
    I hope that our beloved akvarium fishes dream about…
    🙂 beautiful coral reefs and true fish love. (-:

  14. Want to know a trick that I know that works. If your having a nightmare cross your eyes and you will cross your eyes for real and will wake up. Fyi for anyone that's having a night terror.

  15. 0:16 "But dog's brains are relatively similar to ours. What about something way more different from us?"

    Initially, only a sleeping woman can be seen.

  16. I know dogs do have dreams, our dog used to talk in its sleep. little quiet woofs, and move his legs sometimes like hes trying to walk or run.

  17. Too bad you didn't put any video of those fish brain blinkenlights, that would be really interesting to see (totally not suggesting making a fish with RGB lighting with each color indicating a different neurotransmitter)
    Edit: there's a light-up fish brain video:

  18. Before explaining if fish dream, I would like a little elaboration on how on earth someone came up with the idea of looking into it.

  19. It's not hard to believe everything goes through some type of sleep, even plants, and dreams are ways of those with brains to reboot and recharge.. Good thing God didn't make their pain heard to us, or we probably would have a harder time eating the poor things, as well as the other seafood around and plants.

  20. I just started this video with the rem sleep part. A thought is are dreams are so complex but so is a roku, playstaion, an internet tower, cell phones or even our own brain. What if the subconscious is connected with not just the conscious world we live in but also a part like a signal to something when we're asleep. We can talk to eachother threw the air using invisable signals. As the universe expands as it is, whats to say in the center where it came from, the closest intelligent beeings have been around far longer than us. You drop a rock in a placid lake most of the wave will come from the edge of where the rock hit. What if we have signals triggering out subconscious. Allot of subconscious has feeling in it. Like when you have a crush on a boy or girl in class and butterflies fly threw your stomach. 😋

  21. I think that our eyes move because they are controlled by a seperate part of the brain from what produces the dream images and the images are no different from real images which confuses our visual system.

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