Placeholder Image

Subtitles section Play video

  • [♩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]


Subtitles and vocabulary

Operation of videos Adjust the video here to display the subtitles

B1 sleep fish rem neocortex calcium study

Do Fish Dream?

  • 2 0
    林宜悉 posted on 2020/03/30
Video vocabulary