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Why do we have to sleep?

  1. Sep 15, 2013 #1

    I wonder why we have to sleep.

    Physical tiredness can be measured by the amount of milk acid in our muscles.

    But is there an measureable analogy in our brain when it comes to mental tiredness?

    It seems simple enough that if you use the brain too much it will have to rest.

    But why?

    I mean, you eat mainly for energy (and nutricians) and when food energy has depleated it is actually possible to take from the hull, so to speak.

    So energy is available around the clock and even around a couple of weeks (if you're lucky).

    So energy is not the reason.

    Our brain gets tired and needs sleep for another reason.

    This is however only one part of the question.

    The other is, what happens during sleep?

    One indication is the obvious recovery from hungovers.

    You can be really hung over and nothing really changes from the point you wake up to the point you go to bed again.

    The only time it changes is when you have slept for a night. Then you are feeling remakably better.

    This should mean that what happens during sleep is at least maintenance.

    Like the amateur I am I think that energy is focused away from taking care of the inputs from all our sensors (eyes, coordination etc) and is focused toward maintenance instead.

    And if you think about it, the amount of signal processing is probably higher than most of us think.

    One thing is the forward and feedback system from our lems, one other is the amazing "Terapixel" resolution of our eyesight.

    But why is sleep making us so fit for a new day?

    Best regards, Roger
    Last edited: Sep 15, 2013
  2. jcsd
  3. Sep 15, 2013 #2
  4. Sep 16, 2013 #3


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    Basically, if you're moving around, thinking, calculating, predicting, your body is deteriorating faster and your metabolism is working harder to allow maintenance processes to keep things in order, but it's ultimately losing the fight (very slowly). If you go without sleep for too long, you'll start getting open sores and wounds and there are obvious deficits in cognitive ability as well (often the body will even compensate with microsleeps).

    When you rest, you give your whole body a chance to reorganize itself (such as repairing synapses in the brain) because it's not busy supporting the organisms' driving tasks and stock up on readily-available energy reserves.
  5. Sep 16, 2013 #4
    You mean this literally? There's no healing of flesh wounds while you're awake?
  6. Sep 16, 2013 #5


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    I don't know if I would be as bold to say "no flesh healing" but if there is any, it's capability deteriorates with length of time without sleep. But note that the lesions above are not caused by any kind of traumatic injury.

    EDIT: I guess I should note that I remember that paper for its introduction and that it's available for free. The paper's conclusion may seem like it contradicts the large body of knowledge introduced in the introduction, but it really doesn't. It's a very specific type of sleep deprivation that still allows for deep sleep, just not REM sleep.

    In addition to that, there's been papers published contrary to the view that REM has no effect on wound healing (that used a different methodology):

    but it's not a free paper and it studies nicotine and selenium as well so the introduction isn't as holistic as the previous paper (And, yes, it still does REM sleep deprivation independently of nicotine and selenium).

    Anyway, the focus on just REM sleep is another topic. It's a reaction to the over-emphasis on the importance of REM in many processes ( including memory consolidation) in the past.
    Last edited: Sep 16, 2013
  7. Sep 17, 2013 #6
    I'm perfectly willing to accept that certain types of sleep deprivation might interfere with healing, but my question is whether or not we normally heal at all while awake. Your first statement sounded like you might be implying all wound healing always takes place while asleep. That would surprise me if it were true.
  8. Sep 17, 2013 #7
    Because if we don't we die :p
    Good question though,I think I read before that sleeping gives the brain time to do some kind of maintenance to itself
  9. Sep 17, 2013 #8


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    No, degradation refers to not-well-understood molecular processes, most of them believed to be maintenance (though healing is a form of maintenance, no?). I do get the impression that you do heal faster when you sleep. And there certain organizational processes that don't seem to occur during waking time (or at least are much upregulated during sleep). Repair/adjustment of synapses seems to be majorly upregulated during sleep.

    As for the lesions, it may not even be relevant to healing, it may just be the body's ability to hold everything together. There, simultaneously, might be "healing" going on while lesions are forming. It depends on how you define healing experimentally (i.e. the two papers above differ in that and thus their conclusions for REM sleep.)

    Basically, the core molecular networks are so distributed and degenerate in functionality that it's hard to separate processes from high-level functions. So when you have some kind of failures like this, it's system-wide and everything is wonky. The set of processes you define as healing might still be happening, but they also might just be happening because other integrated processes are happening.
  10. Sep 17, 2013 #9
    This is a very interesting discussion!

    I am fully prepared to believe Pythagorian when he kind of says that no healing would be done if we were not sleeping.

    Take an ordinary wound like the one you would get from falling from a bike while riding it.

    I have recently gotten that kind of wound and absolutelly nothing happens to it during day time.

    The only time there seems to be some kind of healing is after sleep.

    This along with my hangover reasoning above kind of proves it for me.

    It would however be interesting to actually test this in a more scientific way. But this cannot be so easily done of course. In fact, I have heard of a person who could not sleep and was hospitolized. After a month without sleep, he sadly died.

    But I am kind of sceptic to the synapsis repairing theory because why would synapsis need to be repaired at all? The only time something is destroyed in the brain is when there has been some kind of stroke. And I don't think "normal life" has that drastical affect on the brain.

    By the way, viewing that fantastic video Bernhardt so thankfully supplied, taught me, among other things, that you actually do not gain more energy than equal to a hot dog bun while sleeping (compared to being fully arest, I guess).

    So we can totally rule out any energy reasoning whatsoever.

    Meaning that we gain no energy sleeping as compared to being awake and we have energy at the time we get sleepy.

    Yet we need to sleep.

    This is so strange.

    Best regards, Roger
    I wonder if I would be more educated if I read those papers :)
  11. Sep 17, 2013 #10


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    I didn't say that though! What I was trying to imply is that it is too absolute of a statement for such a complex system.

    The brain is not in perfect stasis, our bodies are always fighting deterioration. We don't live forever. The brain, being a highly plastic active environment is probably more prone to standard degradation. Evidence of major overhauls (whether repair/adjustments/whatever) comes from this track of research:


    Essentially, fabp7 and psd are two proteins associated with synaptic construction (fabp7 is thought to guide plasma membrane expansion/contraction while psd, or post synaptic density, guides receptor distribution in the post-synaptic cleft).

    They are found to be highly upregulated diurnally (at night). I'm not sure how sleep affects it (I'm not sure if it's been tested) but it happens diurnally absent of light cues.

    Some people say this is part of memory consolidation during REM, but other research has shown that REM deprivation has no effect on memory.
  12. Sep 17, 2013 #11
    I have now read your first to links (I was kind of afraid that their would be long...).

    They contradict eachother. One says that sleeep depravation (SD) does not affect wound healing. The other says that SD (and nicotine) seems to do just that.

    What should I believe?

    One thing that strikes my mind is, do you know what was widely used as a treatment for depression in the past?

    Yes, it was sleep depravation.

    Not so strange if you think about it.

    If you sleep well you are able to think more intricatelly than otherwise...

    Thanks for your reply!

    Best regards, Roger
    Last edited: Sep 17, 2013
  13. Sep 17, 2013 #12


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    what do notice different about their methodologies for scoring healing? (note it's RSD, not general SD... they disturbed their REM sleep only I believe.)

    Maybe they're both right but they say different things based on what they actually measured. Maybe their RSD routines were different. I haven't scrutinized them terribly closely, the important message is in the introduction of the first link that sets up the state of the research.
  14. Sep 19, 2013 #13
    Edit: In interest of not high jacking the thread I'll start a new one shortly.
    Last edited: Sep 19, 2013
  15. Sep 24, 2013 #14
    Theories about why we sleep are still gathering empirical evidences and insights. I'm inclined to agree with restorative theory which is about maintenance and repair, a mechanic could repair components of a complex machine while it is operating and he could do the job better if the entire machine is set on stand-by.

    There is a property of materials we call fatigue resistance, you can hang a certain weight with a wire and can calculate when the wire will break due to fatigue, I think same property applies also to organic cells. And milk acid that accumulates in the muscles and adenosine that accumulates in the brain are sort of early warning system that triggers the homeostasis mechanism and the circadian clock which consequently initiate sleeping.. relieving the weight on cells to avoid failure due to fatigue and to initiate restoration.

    We could go quantum too and infer that sleeping is another tenacious attempt of life to circumvent the inescapable second law of thermodynamics which is entropy :-D

    Btw, brain don't sleep, it's cognitive function is just set on stand-by.
  16. Oct 18, 2013 #15


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    Sleep Drives Metabolite Clearance from the Adult Brain

  17. Oct 19, 2013 #16
    I thought many million years ago when fire wasn't discovered yet, due to the rotation of the Earth, the resultant darkness and the laws of physics it was not possible for good night vision to evolve(excluding bats - they have a different mode of 'vision'). For me it seems clear that without a good amount of photons life is inefficient and this is contrary to the survival of the species(we waste less resources during sleep). It could be that those who did not evolve sleep died off in or before the Cambrian explosion.

    Edit: It seems the OP is of the same type as the question why bears hibernate in winter.
    Last edited: Oct 19, 2013
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