National Geographic

Why Do Babies Twitch in Their Sleep? (Adorable Video Edition)

When I brought my puppy home last August, I knew he would be fun to play with. I had no idea how entertaining he would be when asleep. He dozed constantly, and more often than not, his whole body — legs, tail, lips, eyes, ears — would twitch. This isn’t a quirk of canines. Sleep twitching happens to “literally every mammal that has been looked at”, says Mark Blumberg, a psychology professor at the University of Iowa. Dogs, cats, rats, ferrets, sheep, squirrels — they all twitch. Even whales twitch their flippers. “I have YouTube videos of a guy who recorded his girlfriend’s toes when they twitched,” Blumberg says.

Speaking of videos…(the first one is Blumberg’s dog, Katy):

I undoubtedly spent too much time in the past couple of days doing YouTube searches for twitching babies. What’s funny about many of these videos is the commentary of those behind the camera. They tend to say one of two things: “OMG, look at that spaz!” or, “Awww, he’s dreaming.” And that’s how sleep researchers have traditionally thought of twitches, too, according to Blumberg.

“The sleep field really started off in many ways as an offshoot of Freudian psychoanalysis and the study of dreams,” Blumberg says. “People see these movements and they think, ‘Oh, Fido is chasing rabbits in his dreams.’ But it turns out that that’s almost certainly not the case.” In an engaging new review in Current Biology, Blumberg argues that these sleep twitches actually have an indispensible purpose: to teach a newborn what all of its limbs and muscles can do, and how to use them in concert to interact with the big, wide world.

The first big study to propose this idea was published more than 40 years ago in Science. Howard Roffwarg, then director of the Sleep Laboratory at the New York State Psychiatric Institute, described the behaviors and brain-wave patterns of newborn human babies as they sleep. He noted that a newborn spends “one-third of its entire existence” in a REM state, with intense brain activity and continuous muscle contractions.

“Grimaces, whimpers, smiles, twitches of the face and extremities are interspersed with gross shifts of position of the limbs,” Roffwarg wrote. “There are frequent 10- to 15-second episodes of tonic, athetoid writhing of the torso, limbs, and digits.” Since newborns can barely see, the idea that these spasms are useless byproducts of their dreams is unlikely, he added. What if, instead, twitches play a key role in the development of the nervous system?

That paper has been cited more than 1,000 times, but it took awhile to percolate*. A decade ago, two big Nature papers reinvigorated the idea that sleep twitches are important, Blumberg says. In the first, Swedish scientists reported that in young rats, spontaneous muscle twitches during sleep help program the cells in the spinal cord to carry out the withdrawal reflex. In the second paper, a French group showed that sleep twitches in newborn rats trigger patterned bursts of neuronal firing that are known to be important for motor coordination. Blumberg’s own experiments have found similar things; last year, for example, he reported that newborn rats twitch their whiskers frequently during sleep, and that these twitches drive certain bursts of activity in several brain regions.

Blumberg uses nifty high-speed video to precisely track the jerky movements of baby rats as they fall asleep. He doesn’t use any anesthesia in these experiments, so I asked him how he manages to get the animals to fall asleep on command. “The hard part is keeping them awake!” he said. Turns out newborn rats cycle from asleep to awake every 10 to 30 seconds. The cycle: They wake up, stretch, yawn, kick, and lift their head around. After about five seconds, they suddenly go limp, with no movement other than breathing. Then individual twitches begin — a limb here, tail there. “Then it starts to build, and almost starts to get this real powerful look of epilepsy to it,” Blumberg says. Then they wake up and it starts all over again.

Here are a couple of Blumberg’s videos. The one on the left shows the movements in real time; the one on the right is in slow-motion:

 

To the naked eye, the movements seem random. But Blumberg’s experiments have shown that the flailing is actually quite ordered in space and time. For example, when an animal brings its right elbow in toward its shoulder, there’s a high probability that the left elbow will immediately follow in the same pattern. Similarly, on the same limb, if the shoulder moves in toward the body, there’s a high probability that the elbow would then flex. Blumberg suspects that these predictable couplings are building blocks that help the developing motor system learn more complex behaviors.

“The brain is trying to understand, what are my limbs, how many do I have, and how many joints, and muscles, and how do they all move together?” he says. Once these simple commands are learned, he continues, the brain can use them to learn more complex sequences. “So that later, you can fire off a command somewhere in your mind, and generate a whole series of joint movements that would bring a bottle to your mouth, or make it possible to step.”

Nobody knows for sure how to read this code — that is, how any particular pattern of twitches leads to a specific complex behavior. But Blumberg says the future of figuring this out is with robots. Researchers can design computer simulations of simple neural networks, program in some random muscle contractions, and see what kinds of circuit patterns emerge. For example, roboticists Hugo Gravato Marques and Fumiya Iida of the Swiss Federal Institute of Technology Zurich (who co-authored the new review) have used such simulations to show that twitches help form the spinal cord’s withdrawal reflex — a neat confirmation of the earlier Nature paper. In the future, the robots will get more sophisticated, modeling twitches in multiple joints and multiple limbs, Blumberg says. “These feedback loops all have to be integrated and mapped, and it’s a very difficult thing to study in an animal.”

I asked Blumberg how the rest of the sleep field has responded to these ideas. He said he had just been to a big sleep conference in Baltimore and that, for the most part, sleep researchers still aren’t giving much thought to development. “I can’t tell you how many people have theories about sleep, and they all want to have a grand theory of sleep.” Some people think sleep is for memory consolidation, others that it’s for pruning synapses, or conserving energy, or even just limiting the time we have to make stupid decisions and put ourselves in danger.

But for Blumberg, the question, What is sleep for? is just as silly as, What is being awake for? Just as being awake is a good state for eating, drinking, and reproducing, perhaps sleep just happens to be the best time for consolidating memories, saving energy, and learning motor patterns. “What we have to come up with is the reason why sleep is so conducive for all of those things.”

*

Blumberg wrote a comprehensive historical review of the idea in Frontiers in Neurology 

You can read about other scientists using biological principles to build robots in my 2011 feature in New Scientist

There are 29 Comments. Add Yours.

  1. Kathy K.
    June 20, 2013

    If you think about all the things that we need to be able to do without thinking (such as automatic reflexes) then it makes sense that the body needs to learn these things in an unconscious state.

    Thanks Virginia for this very interesting article. Also, thanks for all the adorably funny video clips.
    Many thanks to scientists/doctors like Blumberg and Roffwarg for all their hard work and research.

  2. ET
    June 20, 2013

    Why does Roffwarg think that dreaming has to include vision? “Since newborns can barely see, the idea that these spasms are useless byproducts of their dreams is unlikely, he added.”

    Why can’t dream use any/all senses?

  3. Chris
    June 20, 2013

    I’m not sure I understand this research, he seems to be saying “Babies twitch to subconsciously learn how to use their limbs”

    This seems to ignore the fact that animals/people twitch into adulthood, where I’d assume we already know how to do these things.

    What about vocalizations? All dogs I’ve ever had, from puppy to adult twitch and vocalize (whimper, whine and bark) in their sleep.

  4. Wallace Gambling
    June 20, 2013

    People should do research before posting their self opinion based on their ignorance. Some adults do not grow out of lots of biological activities, does not mean scientist are wrong when making some investigations.

  5. Rob
    June 20, 2013

    When making investigations? You are a bright one, it is a fair question to wonder about patterns of sleep twitching into adult hood if it is the brain’s way of learning to control limbs.

  6. TeeG
    June 21, 2013

    what a giant waste of time

  7. dave
    June 21, 2013

    What total rubbish. The twitching is part of REM sleep. Watch the eye-lids of the cat, dog or Human. We live in an age of ‘junk science’ where NASA can hold a press conference to declare that they have found DNA composed of non-standard atoms, and claim atrocious and moronic experimental ‘evidence’ is proof.

  8. Blair
    June 21, 2013

    @ET – We do dream with multiple senses, but you cannot dream about things you have not yet perceived. For example, congenitally blind people do not dream with vision/colour, becuase they don’t know colour, never experienced vision… so they dream about smells, textures, etc.

  9. Virginia Hughes
    June 21, 2013

    @Chris — Actually, the twitching goes down considerably as the baby grows up. Yes, adults still twitch, but it’s nowhere near the rate of newborns. So that’s why scientists like Blumberg think it might be related to development. I’m not sure about the vocalizations, but I’ve asked Blumberg what he thinks. Will report back!

    @Dave — Blumberg counts REM eye movements as part of the twitching phenomenon! Don’t see how that makes it “junk” ?!

  10. Virginia Hughes
    June 21, 2013

    @Chris — I asked Blumberg about the vocalizations. Here’s what he said: “Having watched my dog bark in her sleep and watched a lot of videos, it looks to me like the sounds are produced by twitches of the abdominal muscles and diaphragm (and maybe intercostals, the muscles between the ribs). Of course, the sexier alternative is that they are produced by dreams, but there isn’t (and probably cannot be) evidence of that.”

  11. Samson
    June 21, 2013

    @Wallace – just because this scientist explains twitching, doesn’t mean mammals don’t dream on the reg and move while doing so. Thanks for playing

  12. scott
    June 21, 2013

    I have observed different types of behavior in my springer spaniels , when they were in what I thought was the REM state. everything from a friendly greeting complete with wagging tail, to growls snarls and leg movement as if running . I am convinced they are experiencing some sort of dream stimulus.

  13. Chris
    June 21, 2013

    @Dave – “What total rubbish. The twitching is part of REM sleep. Watch the eye-lids of the cat, dog or Human.” Saying that “twitching is part of REM sleep” (which is exactly what Blumberg would say) does not explain anything, since REM sleep is only poorly understood, and the main function of REM sleep is still a question of serious debate in science. The difference between people like yourself and scientists is that the scientists run experiments and test their ideas rather than just labeling things and taking those labels to constitute explanations.

  14. Arnold Mok
    June 21, 2013

    I only know little bits about sleep from portions of Psych 101 and documentaries from Discovery/Nat Geo. However, from personal experience is the combination of ‘everything’ during sleep is so important. I suppose that the twitches of infants of animals to humans are more apparent and it sorta fades to eye twitches/movements. I personally think that the entire environment: temperature, humidity, comfort, level of relaxation, the mattress, the bedding/linen, to even the feeling of: ‘Do you feel safe?’ – has to do a lot with the amount of ‘twitching’ – let alone be whether or not your brain is able to really ‘dream’. This also goes to say that it probably relates to Maslow’s Hierarchy where humans seek to meet our physiological needs, then the ‘home/nest – safety’. It probably means that unless all of the above is met, not only our lives are harder to reach self-actualization, other stresses in everyday life just adds onto the difficulties on moving up the pyramid?

    I’ve also realized that the sleep from when a person that has exerted large amounts of energy during the day whether it’s physical or mentally, the brain and the body absorbs the ‘quality’ of sleep in a much faster pace…

  15. Sandy Holland
    June 21, 2013

    Your theory does not stand up to pragmatic observation.
    How do you account for the fact that every one of my dogs (I have had six) has continued twitching and woofing in their sleep throughout their whole adult lives?

    • Virginia Hughes
      June 21, 2013

      Hi Sandy,
      Please see my earlier comment. Twitching drops dramatically after the juvenile period.

  16. Boise Ed
    June 21, 2013

    Virginia, if that’s so, then our dog must have been one helluva twitcher when he was a pup. He’s 10 1/2 how (we got him at about age 4) and sometimes twitches and yelps up a storm.

  17. Don
    June 21, 2013

    This suggests that we know for a fact that there is no such thing as ‘genetic memories’. Prove it, either way, and then we can begin to understand the reasons for sleep movement.

  18. adam
    June 21, 2013

    When I first read the article I thought it was very interesting, but then there are a couple things I don’t understand. How do twitches help an individual interact with the world if he/she is not conscious of the surrounding world. Also, the coupling of shoulder and elbow movement could mainly be mechanical effects of the movement not related twitches.
    Finally, what is the immediate need or stimulus to trigger these twitches?

    • Arnold Mok
      June 22, 2013

      Adam writes: “What is the immediate need or stimulus to trigger these twitches?”

      Don’t quote me on this, I have slightest idea… but I think it might have to do with we kill/use so much brain cells everyday, every minute, every second – especially when we are very active with our physical/mental activities. It might have to do with how our brain cells starts to repair itself and connecting the synapses between the cells that somehow sends unconscious signals to our muscles that makes us twitch. If you think about it, puppies and babies don’t have their brain completely developed when new born. So, probably they exert huge amounts of effort and energy whenever they’re awake plopping around doing whatever to learn about movements and the world… it’s exhausting!

      Just a maybe… have to ask a doctor/scientist to verify…

      Have a great weekend!

  19. Gerald zuckier
    June 21, 2013

    My dog would twitch up a storm with muffled vocalizations and all, then awake with obvious signs of post-nightmare confusion. Easy to explain as partial failure of the reticular activation system (isn’t it? ) that keeps you paralyzed so you don’t sleepwalk off a cliff. The pattern in movements may just be the pattern of locomotion.That said, REM sleep itself might be related to this hypothesis, because it sure sounds interesting.

  20. Aida Karabu
    June 23, 2013

    I believe that the idea that twitching in sleep because of the development in the muscles and body tissue is possibly right. But, the theory is not complete. There are still wholes in the story. If the reason for twitching is for the organism to learn how the limbs function, then why does it st op at such a young age? At the age of 18 the body is still not fully developed and many muscles are not used. I do not believe this can be the reason. Even though people have tested the theory on other animals, you can’t expect it to be the same for human babies, human babies may in fact just not have control over their limbs at that age and the brain just commands random muscles to move. We have not tested weather that is the reason so we do not know. We can not have a final decision either way.

  21. Virginia Hughes
    June 24, 2013

    A lot of you have asked about adult animals twitching during sleep. Yes, adults twitch, too! But they do it much, much less than babies do. Blumberg thinks the adult twitching is due to continued brain plasticity throughout the lifespan. “This is important because we need to constantly recalibrate our sensorimotor system as we grow, shrink, gain weight, incur brain damage, etc.” he told me.

  22. rose
    June 24, 2013

    I think babies twitching is because babies have not developed completely,mentally or physically . They twitch totally unconsciously, and they cannot control their body very well.

  23. Cynthia Meitle
    June 26, 2013

    But why oh why does my 9-year-old black lab Peppers do these very same things? I’ve been convinced that the motions she goes through while asleep are actually reliving birth, and also the experience of feeding when she was a small pup. When the paws start twitching and she then “runs in place” followed by tiny yelps, I think she is with her brother and sister pups and they are running to eat and yelping with excitement. All in all, it’s extremely fascinating and she just happens to be doing it at this very moment as I type.

  24. Partha Mitra
    June 29, 2013

    Dreaming is associated with spontaneous brain activity. So are the sleep twitches in question. So at some level the brain is “dreaming” when “twitching”. Since there is no objective way of finding out whether the sleeping baby (or the dog) has some level of conscious awareness of this spontaneous brain activity (ie “dreaming”), there are no grounds of judgment either way about “dreaming”. Whether the twitches are helpful for developmental motor learning or not (presumably they are) have no bearing on dreaming per se. Also, the fact that newborns have blurry vision does not provide positive or negative evidence about dreams: in principle the baby could be having visually blurry dreams.

    Sleeping zebrafinches show tail twitches in their sleep, when their brains play out song motor programs. Are they dreaming (ie subjectively conscious of) of singing? Maybe yes, maybe no, but there are no grounds to make scientific assertions either way since the sleeping bird cannot provide a subjective self-report on awakening from this dream-or-non-dream state.

  25. Toria
    July 3, 2013

    This has got me very curious about swaddling. I know a lot of moms who swear that swaddling helps their babies sleep better and longer and the theory is that the baby either feels safer (like in the womb) or doesn’t wake himself up as he otherwise would due to this twitching.
    If full motions are needed to make the neural connections learned in sleep, would swaddling theoretically decrease learning? It is such an age old practice that I can’t imagine it making a big difference, but I’m definitely curious.

  26. S. Quid
    July 21, 2013

    > “People see these movements and they think, ‘Oh, Fido is chasing rabbits in his dreams.’ But it turns out that that’s almost certainly not the case.”

    How does any of this research suggests that they don’t dream (of chasing rabbits or whatever)?

    My dog has chased rabbits. He twitched before he chased rabbits, and twitches still, when he sleeps.

    I have chased dogs. I apparantly also twitch in my sleep. After chasing dogs, I have dreamt of chasing dogs. Before that, I dreamt of other things.

    Sure, my twitching probably has a very good biological reason, but it co-occurs with REM sleep, where dreaming happens. If you want to argue that dogs do not dream, even though they twitch during REM sleep and have a lot more in common with our gene pool than they have differences – then the onus is on you to prove that they do not.

    Occam’s razor, and so on.

    • Boise Ed
      July 21, 2013

      To paraphrase Donovan: “This is the season of the twitch.”… The rabbits running in the ditch … must be the season of the [t]witch …”

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