Sleep May Prepare You for Tomorrow by Dissolving Today's Neural Connections

By Eliza Strickland | April 3, 2009 3:11 pm

sleep fruit flySleep may be a way to sweep out the brain and get it ready for a new day of building connections between neurons, according to two new studies of fruit flies. The studies support the controversial theory that sleep weakens or entirely dissolves some synapses, the connections between brain cells. “We assume that if this is happening, it is a major function, if not the most important function, of sleep” [Science News], says Chiara Cirelli, a coauthor of the first study, published in Science.

Pruning synapses may be a practical necessity to keep the brain from being overwhelmed, says Paul Shaw, coauthor of the second study (also published in Science). “There are a number of reasons why the brain can’t indefinitely add synapses – including the finite spatial constraints of the skull. We were able to track the creation of new synapses in fruit flies during learning experiences – and to show that sleep pushed that number back down” [Telegraph], he says.

In the first study, Cirelli and her colleagues show that proteins found in the synapses build up in fruit fly brains while the flies are awake. Depriving flies of sleep leads to ever-greater levels of synaptic proteins, the researchers show. Levels of the proteins decrease as the flies sleep [Science News]. The researchers couldn’t directly determine synaptic strength because fruit fly brains are too small to allow them to measure electric activity between neurons; however, they say that measuring the proteins is a valid indirect gauge of synaptic strength.

Meanwhile, Shaw’s lab had previously determined that fruit flies sleep longer following social interactions, rather like a human who has been through a busy day. His team then showed that the brains of socially isolated flies contained fewer synaptic terminals than flies subjected to social enrichment, and that the number of terminals decreased in flies that were allowed to sleep. “I think our data shows the first signs of real structural changes,” he said [The Scientist].

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DISCOVER: Mind Over Time asks whether we can alter circadian rhythms
80beats: Sleep Experiment Shows the “Graveyard” Shift Is Aptly Named

Image: Chiara Cirelli. The synaptic markers are low after sleep (left) and high after wakefulness.

CATEGORIZED UNDER: Health & Medicine, Mind & Brain
MORE ABOUT: learning, memory, sleep
  • BandTheory

    I am surprised no one else finds this significant enough to comment on. Sleep, were it not necessary, would be one of the single worst behavior to develop. Imagine electing to have eight hours where you are not eating, mating, avoiding predators.

    And yet we see it conserved across Animalia. It implies that sleep is incredibly significant, and yet we still have no idea what actually HAPPENS during sleep.


    The problem with this article is that it doesn’t answer the question we are all really thinking.. When can we figure out what happens during sleep and how do we replace it so we never have to sleep, or sleep very little at least… I would be able to read alot more science articles…

  • TheThinker

    Sleep is when the subconscious mind turns the conscious mind “off” so that it will not be “interrupted” while it is doing its “housekeeping”. In other words, “linking up” all the newly sensed data/info in temporary/scratch memory with associated data in permnanent memory ….. or resolving queries/problems of the “awake” period. Which gives rise to the old saying of “sleep on it”. Thus, any pruning of synapses would be in the “conscious” or temporary memory area to clear it out or prepare it for the next day’s activity. Just my thoughts on the subject.

  • Claude Belisle

    There are in fact many things worthy of thought. What decides which connections are dissolved? Can this process be directed eventually (think getting rid of horrific experiences). Are the dissolved connections only a representation of “RAM memory” and are they “backed-up” to more permanent memory patterns? Given we forget things over time, is that process similar to the one described (i.e. are the dissolved patterns only new patterns, or do they include older ones “tagged” for deletion)? Should we ever find a way to artificially conduct this “cleaning”, would our need for sleep disappear (i.e. is the function described above the reason we need to sleep)? I’m sure smarter people than I can come up with even more questions.

  • Sean

    Do dreams perhaps stem from the dissolving of these connections? If recent connections are the ones most likely to be dissolved, and dreams often seem to be about recent events. Or maybe dreams stem from the process by which the brain makes a connection permanent?

  • Andrew

    Just to say I very much enjoy sleeping and the idea that it needs to be fixed somehow is a rather surprising one.

  • otakucode

    Claude Belisle: The book “Synaptic Self” is a good resource for understanding how the brain acquires new information and integrates it. The bottom line is that dissolving neuronal connections is as important and constructive as new axonal growth. A dissolved connection does not simply “unlink” two things. It helps relate concepts more closely and precisely. It can define things which are not connected, which is just as important as knowing things are connected. There was a school of thought that believed the brain started out with all possible connections wired up, and that all learning was essentially “remembering” the knowledge that was already stored in the brain by severing extraneous connections. While we now know that this is not the primary method of learning, and that the brain does not begin in early life as completely connected with all knowledge potentially lying dormant, we also know that learning by severing extraneous connections is a very important practice.

  • Aranes

    Wow! I thought that this article was very interesting.

  • kantro

    Wow! Any article that draws neurological conclusions about the human brain from studies of fruit flies is generally difficult to take seriously…

  • CatsAreGods

    This idea is slly.

    We sleep in order to dream.
    We dream in order to prepare our mind for the next day.
    We live with cats so that they can help moderate our dreams.

  • Adam Savage

    [Moderator’s Note: This comment was both offensive and spam, and has been removed.]

  • ugubabba

    The article would explain easier remembering of constant repetitions. Its an darwinistic process – first cancel everything , if it proves useful it will be repeated and therefore not dissolved on the same level trivial learning experiences are.

    I really liked this article.

    It is certainly a pity that some people do not learn, or better learn the wrong things Adam Savage.

  • yaya


  • BandTheory

    The above post by “Adam Savage” is a trojan or virus. It caused Firefox to move all around my desktop and showed some nasty photos. I would ask you to consider removing it.

  • TheThinker

    If synapses are being pruned then how is it possible that one can be reminded of things that happened yesterday, last week or thirty years ago. I mean like, look through a family photo album or an old High School Yearbook ….. and write down all the “memories” that you are reminded of.

    Given the right “trigger” the subconscious mind will locate those old memories and “post” them so that one can consciously “see them”.

  • Mantissa

    People who, late in life, find themselves unable to sleep for extended periods, die. No exceptions. For example, death occurs in patients with fatal familial insomnia between 7 to 36 months from onset. There is no known treatment, no cure.

    Waking from a dream is death to the sub-persona inhabiting the reality of the dreamworld. And waking from life is what we call death. Our world is just a temporary fragment in an infinite ladder of dreams.

  • Seb

    otakucode, that was was really brilliant, it makes so much sense. Out of curiosity, where would one find more people who think like you?

  • Isaac Marion

    Fruit flies experience “social enrichment”? Are fruit flies getting together on weekends to play volleyball and discuss books they’re reading? Why wasn’t I invited?

  • Elegiac View

    I would be against the idea of attempting to reproduce the results of sleep so that we would no longer find it necessary to sleep.

    Yes, I admit, I am a person who would rather function without sleep, because then I could get so much more done… Then again, I’m also the sort of person who has been known to neglect meals for the same reason. With that in mind, I will ensure that sleep is as essential as food. Would we endeavor to find something that replaces food? No, because that would be impossible. Therefore, I don’t believe we could successfully trade sleep for some kind of mental processing instead. It would deplete the whole purpose of sleep, which is probably to smooth out our minds and provide readiness for a new day. (If you don’t look at it in a purely scientific way, that is.)

  • Verena

    “The Thinker” – you need to learn more about neuroscience, as you seem to directly equate neural connections with memories.

  • beach bum

    This is so interesting! The pruning of synapses (or connections between brain cells) probably affects the kind of inconsequential stuff that happens on a daily basis. Remembering every bit of trivia from every single day of life would obviously slow us down long term. But episodes that are repeated or highly emotionally charged are obviously stored on a more permanent basis.

    I always thought of sleep as an opportunity for the brain to synthesize that day’s information and store it, but it is interesting that it might also be an opportunity for us to forget things! Thanks for the info!

  • Petros Kasanovas

    And than again fruit flies don’t have a hippocampus or a cerebral cortex so the entire analogy to humans is questionable.

  • K

    Pruning. Like that idea. Dreams could be the trashcan! Need to replicate study results in humans though. True what Petros K says: fruit flies don’t have the same brain components as humans. Just be careful using those MRI’s and other radiation scans on people. They can cause cell damage over time.


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