Why sleep? Scientist delves into one of science's great mysteries
August 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 memory 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 platypus 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 sleeping 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 sleep 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
3 hours ago
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.
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.
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.
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 ;)
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.
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
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.
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 :)
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.
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:
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 ).
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.
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.
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.