Why sleep? Scientist delves into one of science's great mysteries

Aug 20, 2009 By Mark Wheeler

(PhysOrg.com) -- Bats, birds, box turtles, humans and many other animals share at least one thing in common: They sleep. Humans, in fact, spend roughly one-third of their lives asleep, but sleep researchers still don't know why.

According to the journal Science, the function of sleep is one of the 125 greatest unsolved mysteries in science. Theories range from brain "maintenance" — including consolidation and pruning — to reversing damage from oxidative stress suffered while awake, to promoting longevity. None of these theories are well established, and many are mutually exclusive.

Now, a new analysis by Jerome Siegel, UCLA professor of psychiatry and director of the Center for Sleep Research at the Semel Institute for Neuroscience and Human Behavior at UCLA and the Sepulveda Veterans Affairs Medical Center, has concluded that sleep's primary function is to increase animals' efficiency and minimize their risk by regulating the duration and timing of their behavior.

The research appears in the current online edition of the journal Nature Reviews Neuroscience.

"Sleep has normally been viewed as something negative for survival because sleeping animals may be vulnerable to predation and they can't perform the behaviors that ensure survival," Siegel said. These behaviors include eating, procreating, caring for family members, monitoring the environment for danger and scouting for prey.

"So it's been thought that sleep must serve some as-yet unidentified physiological or neural function that can't be accomplished when animals are awake," he said.

Siegel's lab conducted a new survey of the sleep times of a broad range of animals, examining everything from the and the walrus to the echidna, a small, burrowing, egg-laying mammal covered in spines. The researchers concluded that sleep itself is highly adaptive, much like the inactive states seen in a wide range of species, starting with plants and simple microorganisms; these species have dormant states — as opposed to sleep — even though in many cases they do not have nervous systems. That challenges the idea that sleep is for the brain, said Siegel.

"We see sleep as lying on a continuum that ranges from these dormant states like torpor and hibernation, on to periods of continuous activity without any sleep, such as during migration, where birds can fly for days on end without stopping," he said.

Hibernation is one example of an activity that regulates behavior for survival. A small animal, Siegel noted, can't migrate to a warmer climate in winter. So it hibernates, effectively cutting its energy consumption and thus its need for food, remaining secure from predators by burrowing underground.

Sleep duration, then, is determined in each species by the time requirements of eating, the cost-benefit relations between activity and risk, migration needs, care of young, and other factors. However, unlike hibernation and torpor, Siegel said, sleep is rapidly reversible — that is, animals can wake up quickly, a unique mammalian adaptation that allows for a relatively quick response to sensory signals.

Humans fit into this analysis as well. What is most remarkable about sleep, according to Siegel, is not the unresponsiveness or vulnerability it creates but rather that ability to reduce body and brain metabolism while still allowing that high level of responsiveness to the environment.

"The often cited example is that of a parent arousing at a baby's whimper but sleeping through a thunderstorm," he said. "That dramatizes the ability of the human brain to continuously process sensory signals and trigger complete awakening to significant stimuli within a few hundred milliseconds."

In humans, the brain constitutes, on average, just 2 percent of total body weight but consumes 20 percent of the energy used during quiet waking, so these savings have considerable adaptive significance. Besides conserving energy, sleep invokes survival benefits for humans too — "for example," said Siegel, "a reduced risk of injury, reduced resource consumption and, from an evolutionary standpoint, reduced risk of detection by predators."

"This Darwinian perspective can explain age-related changes in human sleep patterns as well," he said. "We sleep more deeply when we are young, because we have a high metabolic rate that is greatly reduced during sleep, but also because there are people to protect us. Our patterns change when we are older, though, because that metabolic rate reduces and we are now the ones doing the alerting and protecting from dangers."

Source: University of California - Los Angeles

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SincerelyTwo
5 / 5 (2) Aug 20, 2009
Maybe there's some mechanisms in our being which behave much like rechargeable batteries. And what ever that chemical reaction is, which provides us with what ever we need to remain alert, needs to be recharged periodically - so obviously sleeping lowers demand for said reaction to occur, and our 'buffers' are regenerated.

So the question is, what is made available in larger amounts while we are awake vs. when we are asleep? That information may* allude to what it is which is requiring us to sleep.

I'm sure sleeping exists to begin with since being awake and active has such high cost in energy. Perhaps we don't convert food in to energy very quickly, and we run through our storage before it's converted from other sources (thus rest!)?

And while you scientists are at it, figure out how to stop sleep paralysis, it's pissing me off.
Birthmark
5 / 5 (2) Aug 20, 2009
And what ever that chemical reaction is, which provides us with what ever we need to remain alert, needs to be recharged periodically - so obviously sleeping lowers demand for said reaction to occur, and our 'buffers' are regenerated.

I think that just the fact we're able to slightly understand why we sleep opes doors for resolving time issues and the opportunity to have to never sleep again. Could you imagine if over time they find out how to make our bodies recharge over a period of 2 hours, so sleeping goes from 8 hours a day to 2, and eventually we'll be recharging constantly, needing no sleep.
Alexa
1.8 / 5 (5) Aug 20, 2009
The importance of sleeping is in point, we cannot learn and train neural network at the same time due the positive feedback of network during learning (during training phase we cannot remain productive and vice-versa). From AWT perspective neural network is system of electroacustic solitons spreading along predefined paths by principle of least action, which can solve complex optimization problems, i.e. to think.

To learn such network new capabilities it's necessary to detach it from external stimuli and let it evolve in its own chaotic simulations of reality, which is what the dream REM phase is called. During this period network is becoming more dense and complex at the place of soliton trajectories, which were used most often during this simulation like dynamic terminal box.

The principle of neurosis is in usage of learning mode of network in vigilant state, which often result from lack of time for sleeping.
LucFerris
5 / 5 (5) Aug 20, 2009
Perchance to dream?
Truth
not rated yet Aug 20, 2009
When we exercise, say a bicep muscle, we can only do it for a certain amount of time before it begins to hurt, or "burn", so we stop, giving the circulatory system time to carry away the lactic acid that builds up in an active muscle. When that's done, we can then exercise the muscle some more. Could this process also be active for our brains, which accumulate waste products (burn) during waking hours, and therefore needing some down-time (sleep) so that the blood can carry away those waste produces?
Ulg
1 / 5 (2) Aug 21, 2009
It is just for the sake of efficiency that we evolved all those irresistible urges to crawl up and wait for the sun to be shining. But I have a somewhat unique perspective on that. Right now is much like my young childhood- I do not get enough sleep to satisfy my urges. But there was a point- that I would routinely back to back be awake and fully productive for two weeks at a time. Not one yawn, nor droopy eyelids- not once would I be distracted by being tired. I took great care of my body nutritionally and worked out vigorously, all the while my test scores either remained or gained. I've heard a lot of nonsense that a person cannot be awake longer then X days or they will die, but I am sure that any study that came to that conclusion has numerous confounding factors that attributed, namely stress.

I'd bet my bottom dollar that one day either evolution or science will make sleep nothing more then a vestigial trace of homeostatic mechanisms.

For most people that have ever performed an all nighter (1 days of being awake) they might have at one point gotten a second wind, where one moment they are about to fall asleep and the next minute they are not just alert but refreshed. And while it may only last 10 minutes, it might last till the next time they would normally go to sleep. And a normal nights sleep will do them just fine the next day. Nothing magic happened- they just overcame their instinct to sleep which is setup by numerous homeostatic mechanisms and psychologies, maybe their body looked over a list and said- well all of our requirements are met, so continue normal operation.

For now I am off to submit to the urge to sleep, 4 hours a night seems to do me nicely 13 years later, and quite a bit more out of shape ;)
Soylent
5 / 5 (2) Aug 21, 2009
...so we stop, giving the circulatory system time to carry away the lactic acid that builds up in an active muscle..


Lactate build up('lactic acid') is not the cause of weakness, burning sensation during exercise, DOMS or muscle acidosis(hydrogen ion concentration is an independent variable, most of the acidity is thought to come from breakdown of ATP into ADP and ADP into AMP).

Lactate is not some toxic waste product, it is a harmless byproduct. It does not get carried away by blood circulation. Lactate builds up because there is insufficient oxygen for the citric acid cycle to operate at sufficient rates. Instead of allowing pyruvate to participate in the citric acid cycle it is temporarily converted to lactate without using oxygen, providing energy. As soon as enough oxygen comes back the muscle cells begin to oxidate lactate back into to puryvate(uses energy) which is then successively oxidized in the citric acid cycle to water and CO2.
bugmenot23
not rated yet Aug 21, 2009
Sleeping does not give "reduced risk of detection by predators" if even one member of the group snores like a freight train.
diva4d
not rated yet Aug 21, 2009
Doesn't make sense to me. If it was as proposed by the article, why do we HAVE to sleep or suffer serious consequences? If it had to do with metabolic efficiency, I would think that if we had no shortage to eat, we would not need sleep. And as for minimizing risk - ridiculous. It would be much better if the organism could stay quietly alert while predators prowl.
Mercury_01
5 / 5 (2) Aug 21, 2009
Ill tell you why we sleep, its cause we get tired of being awake.
El_Nose
not rated yet Aug 21, 2009
do you know how boring late night programming is --

anyway muscles need time of inactivity to repair themselves and you form memories better if you ' sleep on it' i am not in favor of giving up my bed just yet -- if ever
defunctdiety
2.3 / 5 (3) Aug 21, 2009
the opportunity to have to never sleep again

This sounds like the worst existence ever.

Sleep, and more specifically dreaming, is one of the greatest things about being alive, IMHO. It's perhaps the one natural (non-drug induced) state where you can, uninhibited by the trappings of your senses and the material world, tap into the infinite pool of energy that is all of existence. Never sleeping again would be my Hell.
zevkirsh
3 / 5 (2) Aug 21, 2009
you cant answer the question of why humans sleep at a very deep level until you can first answer why bacteria sleep. then work your way up the list. almost all organisms sleep, the question is how and why??
Birthmark
1 / 5 (1) Aug 21, 2009
Sleep, and more specifically dreaming, is one of the greatest things about being alive, IMHO. It's perhaps the one natural (non-drug induced) state where you can, uninhibited by the trappings of your senses and the material world, tap into the infinite pool of energy that is all of existence. Never sleeping again would be my Hell.




Yes I absolutely love dreams and dreaming, but I don't like that by the time I'm 20 that I've slept 6-7 years of my life away that could have been used for many other useful things and fun things in the natural world. If they have the technology to stop sleeping they'll have a device, medicine, or something that induces it as well, so occasionally if you want to dream you'll be able to.



P.S. I'm sorry life is such a hell for you. I'd pick it over dreaming any day. Maybe that's why the world is in such a bad state, we like our delusions over reality :)

almost all organisms sleep[/q[
Very true but sharks don't sleep, maybe we can learn from them as well.
Dreadneck
3 / 5 (2) Aug 22, 2009
It seems to me that removing the need for sleep could have a hugely negative impact on the environment and our quality of life. People consume far more energy, food and resources and produce more waste in waking life than during sleep. Just something to consider.
thales
not rated yet Aug 22, 2009
Has anyone here tried Modafinil? I've heard you can stay up for days on it with little loss of alertness.
noneyet
not rated yet Aug 22, 2009
I noticed as an adult when I owned a dog (that was very alert), that I slept deeper, relying on his ability to filter out threatening sounds.
Joey_Tavares
5 / 5 (1) Aug 23, 2009
'Why' we sleep - that is a silly question.

A bazillion years ago, when all life on Earth was single celled photo-reliant organisms, EVERYTHING went to 'sleep' during that part of the planet's rotations that was in darkness.

A bazillion years later, the conglomerate 'single-cell' organized organisms still 'go offline' when the sun goes down.

Jeez.

antigoracle
1 / 5 (1) Aug 23, 2009
zzzzzzzzZZZZZZZZZ
MongHTanPhD
not rated yet Aug 23, 2009
RE: How/why we sleep!?

you cant answer the question of why humans sleep at a very deep level until you can first answer why bacteria sleep. then work your way up the list. almost all organisms sleep, the question is how and why??


I thought this is a very observant and insightful query that deserves a response that has not been pursued thoroughly by the scientific community before!

This is because most scientists have not been pursuing the sleep question from a fundamental biological and physiological perspective; in and by which most organisms will sleep in response to their respective circadian rhythms or sleep-wake cycles or corporeal homeostasis in general.

Briefly, homeostasis is a vital survival mechanism that is essential to all living entities -- ranging from single-cellular to multi-cellular organisms, like humans: the most complex living things of all things living on Earth.

Biochemically and physiologically, homeostasis may vary and operate differently in each cell types (including bacteria) and at different organism and structural levels -- especially in humans, homeostasis is regulated and controlled by our central nervous system (including our brain) as the homeostatic system that consists of the autonomous or involuntary nervous systems (which operates during both the sleep-wake cycles) and the voluntary nervous systems (that are active only during the waking moments, thus enabling us to find foods (or energy) and/or mates (or partners), etc, for survival)!

Thus, several sleep-wake questions (especially 1-3 below) might be (metaphorically and laterally) explained as follows:
Maybe there's some mechanisms in our being which behave much like rechargeable batteries. And what ever that chemical reaction is, which provides us with what ever we need to remain alert, needs to be recharged periodically - so obviously sleeping lowers demand for said reaction to occur, and our 'buffers' are regenerated.[1]

So the question is, what is made available in larger amounts while we are awake vs. when we are asleep? That information may* allude to what it is which is requiring us to sleep.[2]

I'm sure sleeping exists to begin with since being awake and active has such high cost in energy. Perhaps we don't convert food in to energy very quickly, and we run through our storage before it's converted from other sources (thus rest!)?[3]

And while you scientists are at it, figure out how to stop sleep paralysis, it's pissing me off.[4]


Whereas the question 4, regarding sleep paralysis, that would be a natural phenomenon that is regulated and controlled by the genetic makeup of the autonomous neurons located in the area between our brain and brainstem. During sleep, our sensory-motor nervous systems will be blocked off at this region autonomously, thus giving us a sense or feeling of paralysis during our REM dream states.

Specifically, in the case of frequent sleep paralysis, it may be caused by one's own stressful, anxiety-driven sleep-wake cycles -- especially associated with one's heightened autonomous neuro-endocrino-cardiac system. [For more discussions, please see my book Gods, Genes, Conscience (linked below) Chapter 4 The Human Life, Mind, Dreams, Intelligence, and Conscience; especially section 4.7 Dreams and Stresses/Distresses; and 4.8 The REM Sleeps and Dreams; etc.]

Best wishes, Mong 8/23/9usct1:39p; practical science-philosophy critic; author "Decoding Scientism" and "Consciousness & the Subconscious" (works in progress since July 2007), "Gods, Genes, Conscience" (2006: http://www.iunive...95379907 ) and "Gods, Genes, Conscience: Global Dialogues Now" (blogging avidly since 2006: http://www2.blogg...50569778 ).
antialias
5 / 5 (1) Aug 23, 2009
How about the recuperative effect of sleep? An animal can use more energy (for foraging, running away, etc.) if it sleeps periodically than it could if it stayed awake all the time. In effect 'wearing itself out' over the active period with above-par exertion while recovering during the sleeping period.
GregHight
not rated yet Aug 24, 2009
Be careful of what you wish for. If humans find away to avoid sleep, do you think all that extra time is going to be used for rest and relaxation or pursuing your favorite hobby?

You will have to devote more and more of you "sleeptime" toward work or school in order to keep up with your over achieving peers. You will also need to work more to cover the increased cost of having an extra 8 or 9 hours of living, working etc.

It sounds like an dream come true and I'm not sure that I could resist if it became available. I'm not sure the world would be a better place without humans sleeping. I somehow doubt it.
defunctdiety
not rated yet Aug 24, 2009
P.S. I'm sorry life is such a hell for you. I'd pick it over dreaming any day. Maybe that's why the world is in such a bad state, we like our delusions over reality :)

Actually I just recognize and utilize sleep as the significant and beautiful altered state of consciousness that it is. I enjoy sleeping and I enjoy waking, both in very different ways. It's really tragic that you don't gain or even percieve any benefit from sleeping, seeing as it is 1/3 of your life. So you express sympathy for me, but you're the one who's wasted 1/3 of your life.

P.S. The world is in such a bad state because a significant portion of people are, by nature, greedy and selfish. And they are unable to overcome that, probably because they don't do enough self-examination and reflection.
denijane
not rated yet Aug 27, 2009
Sorry but that article is nonsense. The only thing I agree with is that sleep isn't putting us at disadvantage. Animals and humans are all very careful when and where they fall asleep, so one can say that sleep actually reduce the risk of being killed/eaten and so on.

But the article misses something very important-if the only reason why we sleep is to decrease power consumption of the brain and reduce risk, then why at present days, when power isn't a problem for us-developed societies can eat as much as they need and we usually don't risk being eaten at all, then why we still sleep? There is absolutely no evolutionary reason to fall asleep, but still, if you don't sleep, you go crazy. And insomnia is one of the biggest curse you can get-you either get not attention at all and you spend your nights in misery; or you get stuffed with pills that reduce your ability to dream and you get other kind of misery. I am periodic insomniac and you can trust me on this one.

And of course, I also love sleeping. I love dreaming, especially lucid dreams. They are so powerful and give you the sense of wholeness.

I think as always, sleep is underestimated by science and I simply cannot understand why some people refuse to admit that a process may serve more than one purposes. Because sleep is the perfect example for such process.

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