Why Do We Sleep? Exploring the Science and Theories Behind Our Need for Rest

[rodsika]

What is you best guess or has science already solved it?

 

[wuliheron]

There isn't any clear scientific explanation yet, but a lot of good evidence has been accumulated. When deprived of sleep and dreaming people will eventually hallucinate and sleep is when the body grows and rejuvenates itself the most including the nervous system and memory. Thus it appears to have significant physiological purposes.

My own guess is it also serves to keep animals from harm. Depression, for example, is thought to be an adaptation to illness and wounds. It encourages animals to seek out a quiet hiding place and lay around for days licking their wounds so they can heal. Likewise sleep keeps animals resting in one spot during the time of day when they are most vulnerable. The tradeoff is they are also less alert, but more alert than you might assume. People, for example, tend to snore and make other noises in their sleep in direct proportion to the ambient noise level as a way to keep themselves asleep, while still remaining alert to strange noises. Only a for a few moments at a time during the night are they in such a deep sleep that strange noises cannot wake them readily.

 

[davenn]

well the first obvious though would be, that's its the body's natural way to rest and recuperate...

one www site stated ...

Why do we sleep?

So why do we sleep? This is a question that has baffled scientists for centuries and the answer is, no one is really sure. Some believe that sleep gives the body a chance to recuperate from the day's activities but in reality, the amount of energy saved by sleeping for even eight hours is miniscule - about 50 kCal, the same amount of energy in a piece of toast.

We have to sleep because it is essential to maintaining normal levels of cognitive skills such as speech, memory, innovative and flexible thinking. In other words, sleep plays a significant role in brain development

Dave

 

[rodsika]

what animals don't sleep? it is said bacteria sleeps too.. but isn't it the heart of living things keeps beating.. heart cells never sleep right?

 

[Rooted]

Heart cells never stop, but then no cells in the body ever stop, really, until they die. I'm not sure how you would define sleep in a single celled organism. Certainly even primitive organisms have circadian rhythms, which might nearly qualify? http://ccb.ucsd.edu/

It seems that genes associated with DNA repair are kicked up a gear during sleep, so maybe DNA maintenance is one of the (many?) reasons for sleep, and that would be something desirable to all but perhaps the shortest lived of organisms. http://neuroscience.mahidol.ac.th/intranet/2011/Allan Hobson_The Neurobiology of Sleep.pdf

 

[RabbitWho]

well the first obvious though would be, that's its the body's natural way to rest and recuperate...

one www site stated ...



Dave

That's like saying "why do we eat" - "because we're hungry". "Why do we sleep?" - "because we're tired."

The body doesn't actually need sleep, it's the brain that needs it. And yet the brain is very active when we sleep.


Berkeley have free lectures on the topic of sleep online on their webcast. I've listened to them all but I still can't really answer this question. (Listen to them with VLC player and increase the sound to 2x, because the lady speaks incredibly slowly)

Our brainwave patters change when we sleep, we have different phases of sleep and it seems all of them are essential, if you are somehow deprived of one (by being woken up) your sleep cycle will alter to make sure you get more of it next time. REM seems to be the most important. During REM your brain shows "alpha waves" which people also exhibit when they meditate . People dream during all phases of sleep, not just REM. Dreams seem to have a function as well, all mammals do it. (I don't know about other creatures) I mentioned here in another thread that they took a mouse and ran him through a maze while he was being read with an (I think) EEG. When he went to sleep afterwards the EEG gave the same readouts, so they knew he was dreaming about running through the maze, and you could actually see the readings from the path recreated turn for turn, he was running through it systematically.

If people study and then go to sleep they will remember the information better than if they didn't sleep or if they revised and didn't sleep.
If you don't sleep within 12 hours of the study usually this benefit is lost, (which sucks because we all know the best time to study is the morning and it's not exactly easy to take a nap in the middle of the day)

They actually did a really horrible test on some poor unfortunate rats where they wouldn't let them sleep just to see if they'd die from sleep deprivation, and they did, after 16 days.

All of this info is from the Berkeley webcast. A lot of it's really interesting, there was a lot of unscientific hippy stuff as well, but that was interesting in it's own right.

Heart cells never stop, but then no cells in the body ever stop, really, until they die. I'm not sure how you would define sleep in a single celled organism. Certainly even primitive organisms have circadian rhythms, which might nearly qualify?

They said on the webcast that simple organisms have periods of high activity and periods of low activity. They don't go into detail, the obvious question would be whether these periods of low activity followed a cycle similar to sleep or whether they just corresponded to a drop in temperature (night) or a lower abundance of food which cased the organism to "rest" just because reactions in its body were hindered.

 

[phyzguy]

Interestingly, birds can put one hemisphere of their brain to sleep while the other hemisphere remains awake and alert. So whatever brain function it serves can be done one hemisphere at a time. Below is a wiki entry on this.

http://en.wikipedia.org/wiki/Unihemispheric_slow-wave_sleep

 

[rodsika]

Two days ago I only slept for one hour, the next day.. i was so fatigued, and tired easily. If sleeping simply supported the brain, how come the body feels fatigued? You would say the brain controls the body. Well. Body impacts the brain too. In many studies. Lack of sleep also affects the immune system. So I think we must first study what is the origin of the subjective feeling of fatigue? How is the the qualia of fatigue produced and located (the body feedback mechanism and actuators)? This is related to the reason why we sleep.

 

[Pythagorean]

Interestingly, birds can put one hemisphere of their brain to sleep while the other hemisphere remains awake and alert. So whatever brain function it serves can be done one hemisphere at a time. Below is a wiki entry on this.

http://en.wikipedia.org/wiki/Unihemispheric_slow-wave_sleep

Dolphins too. They're said to sometimes swim in circles during this state.

 

[Rooted]

I was taught that one of the reasons that we sleep was to allow the mitochondira to replenish depleted ATP stores. Adenosine (the breakdown product of ATP) serum levels are known to increase during waking hours and be a factor in promoting sleep (http://www.nature.com/nrn/journal/v11/n8/box/nrn2868_BX1.html ). I think caffiene works by blocking adenosine receptors, if I remember rightly. ( http://healthysleep.med.harvard.edu/glossary )

Here is some evidence about ATP brain concentration levels increasing during sleep too - but only in the bits of brain that are actually 'asleep'. Perhaps it could be likened to defragmenting a hard disk, in that any progrems being used do not get defragmented? http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2917728/

 

[RabbitWho]

Two days ago I only slept for one hour, the next day.. i was so fatigued, and tired easily. If sleeping simply supported the brain, how come the body feels fatigued? You would say the brain controls the body. Well. Body impacts the brain too. In many studies. Lack of sleep also affects the immune system. So I think we must first study what is the origin of the subjective feeling of fatigue? How is the the qualia of fatigue produced and located (the body feedback mechanism and actuators)? This is related to the reason why we sleep.

Well there's two questions

Why do we sleep at all?
Why do we sleep rather than doing something else?

We know that our cells need inactive periods for example, but why can't we take them in the 10 minutes when we're waiting for a bus or in the 10 hours some people spend watching TV a day. Why is it that you can spend the whole day sitting and yet you body is exhausted if you don't sleep?

This is why I think of it as being something the brain needs, but yeah, you're completely right, it's all connected.

I was taught that one of the reasons that we sleep was to allow the mitochondira to replenish depleted ATP stores. Adenosine (the breakdown product of ATP) serum levels are known to increase during waking hours and be a factor in promoting sleep (http://www.nature.com/nrn/journal/v1...n2868_BX1.html ). I think caffiene works by blocking adenosine receptors, if I remember rightly. ( http://healthysleep.med.harvard.edu/glossary )

Here is some evidence about ATP brain concentration levels increasing during sleep too - but only in the bits of brain that are actually 'asleep'. Perhaps it could be likened to defragmenting a hard disk, in that any progrems being used do not get defragmented? http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2917728/

That's really interesting! I didn't know that.

To me this is a perfect answer to why we sleep at all, it's one very good reason. But it's no reason at all for "Why do we sleep rather than doing something else?". And sleep is so complicated and involves so many different types of brain wave patterns and it's such a strange experience and it's so dangerous for a wild animal..

 

[rodsika]

I was taught that one of the reasons that we sleep was to allow the mitochondira to replenish depleted ATP stores. Adenosine (the breakdown product of ATP) serum levels are known to increase during waking hours and be a factor in promoting sleep (http://www.nature.com/nrn/journal/v11/n8/box/nrn2868_BX1.html ). I think caffiene works by blocking adenosine receptors, if I remember rightly. ( http://healthysleep.med.harvard.edu/glossary )

Here is some evidence about ATP brain concentration levels increasing during sleep too - but only in the bits of brain that are actually 'asleep'. Perhaps it could be likened to defragmenting a hard disk, in that any progrems being used do not get defragmented? http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2917728/

When I don't sleep. I can feel my body heating up the next day. Heating up means the blood circulates faster giving me feeling of more heat. So not only in the brain but it seems the muscles need something in sleep.. somethat that can only be refleshed or recharged during sleep. Depleted ATP? but if one just stay still at bed without actually sleeping.. it doesn't work too.. one has to actually lose consciousness for the muscles to charge up... but why?

 

[Ryan_m_b]

We know that our cells need inactive periods for example, but why can't we take them in the 10 minutes when we're waiting for a bus or in the 10 hours some people spend watching TV a day. Why is it that you can spend the whole day sitting and yet you body is exhausted if you don't sleep?

Have you read about circadian rhythms? There are a variety of biological processes that operate in cycles, in many species (including bacteria) these processes seem to be roughly in sync with each other and with the 24 hour day.

If you're looking for an evolutionary answer as to why we sleep I'm unaware of the current research in the field but here is a journal dedicated to the subject a quick google brought up.

 

[rodsika]

Can anyone show studies or proof that all the energies of muscle movement come from ATP stores? I think I read an article before that they are not enough.. like the sodium, potassium, etc. pumps in the cell surfaces needed so much ATPs that majority of them are used them that the rest need other sorts of energies... and some suggest solitons or davydov solitons are used by muscles for movements.. what is the consensus of this?

 

[mazinse]

yeah other than ATP, you got CTP, GTP, TTP, UTP, but mostly ATP, and there is phosphocreatine

 

[Pythagorean]

what about NAD/NADH?

 

[rodsika]

what part of the brain that says this arm or feet is mine and belongs to me? lack of sleep can tires it such that it's like there is disconnection between them.. maybe this is the origin of fatigue? lack of sleep can produce fatigue.. so sleeps seems to benefit this part of brain that says the body part is yours... maybe the pariental lobes?

when half of dolphin brain is asleep, the side of body connected with it goes limp too such that the dolphin swim round and round... is there an animal or organism where the brain is asleep but the whole body completely active (and not limped)?

 

[mazinse]

what about NAD/NADH?

lol and FADH oh i guess NADPH loses the race

 

[rodsika]

i know this is dumb question but for birds which have one side of brain sleeping at a time and only one wing flapping.. how can they stay afloat in air?

 

[RabbitWho]

i know this is dumb question but for birds which have one side of brain sleeping at a time and only one wing flapping.. how can they stay afloat in air?

Who says there's only one wing flapping?

My first instinct was to say "they don't sleep while flying" but then I remembered migratory birds.

 

[Drakkith]

There's a difference between REM and NREM sleep. In NREM sleep your body doesn't lose it's ability to move your muscles. If birds are flying and only one half of their brain is sleeping then I would expect that they are in NREM sleep. In fact I think I remember reading that REM cannot occur unless both sides of the brain are sleeping at the same time.

 

[rodsika]

So there seems little mystery left about why we sleep.. but why is there no consensus of the real reason we sleep?

The consensus of this board is it has to do with dna programming and the brain. Anyone has counterarguments to it?

 

[Ryan_m_b]

So there seems little mystery left about why we sleep.. but why is there no consensus of the real reason we sleep?

Because we have yet to understand all the processes that occur wrt to the human circadian rhythm. Once we have a good enough understanding of that and of similar animals we will probably be able to formulate solid ideas of how it evolved.

The consensus of this board is it has to do with dna programming and the brain. Anyone has counterarguments to it?

Where did you get "DNA programming" from?

 

[RabbitWho]

So there seems little mystery left about why we sleep.. but why is there no consensus of the real reason we sleep?

The consensus of this board is it has to do with dna programming and the brain. Anyone has counterarguments to it?

Where did you get "the brain" from?

The brain? What about our souls? surely dreaming is the wandering of the soul through the spirit realm.

 

[Drakkith]

Where did you get "the brain" from?

The brain? What about our souls? surely dreaming is the wandering of the soul through the spirit realm.

Souls have nothing to do with science and cannot be discussed here on PF.

 

[skeptic2]

If this topic has been exhausted I have a question about why we sleep 7-8 hours. Humans existed for 10s of thousands of years before they controlled fire and the environment is very dark from 1/2 hour after sunset to 1/2 before sunrise. Why isn't our sleep period closer to 11 hours? What did humans do for those 3 hours every night without light?

 

[rodsika]

Because we have yet to understand all the processes that occur wrt to the human circadian rhythm. Once we have a good enough understanding of that and of similar animals we will probably be able to formulate solid ideas of how it evolved.

Where did you get "DNA programming" from?

What I meant was it was a a biological organism requirements... and since all organisms are controlled by DNA.. then it was an appropriate term.

Anyway. I read that the smaller an animal is.. such as rats, the longer they sleep.. for example.. rats sleep 15 hours a day while dogs and cats sleep more than 8 hours... while elephants sleep only 4 hours.. I read there a direct correlation between the need for sleeps and size of animals.. something to do with metabolism.. the bigger an animal, the smaller its metabolism... so less sleep.. but what has sleep got to do with mitochondria of the entire organism.. not just the brain? unless for those who believes it benefits the brain only, please explain the above observations like correlations of size of animals and sleeping requirements.

 

[Drakkith]

If this topic has been exhausted I have a question about why we sleep 7-8 hours. Humans existed for 10s of thousands of years before they controlled fire and the environment is very dark from 1/2 hour after sunset to 1/2 before sunrise. Why isn't our sleep period closer to 11 hours? What did humans do for those 3 hours every night without light?

If I'm not mistaken I think the recommended sleep length is more like 8-9 hours. That would fit more in line with the 13-14 hours per day that you have light.

 

[rodsika]

http://discovermagazine.com/2009/apr/22-new-theory-about-why-sleep-maintain-immune-system/

Sleep has so many vital functions that it may not just be about the brain and making it alert.

If anyone has encountered biochemical system being fabricated in labs and requiring sleep too.. let me know..

 

[RabbitWho]

What I meant was it was a a biological organism requirements... and since all organisms are controlled by DNA.. then it was an appropriate term.

Anyway. I read that the smaller an animal is.. such as rats, the longer they sleep.. for example.. rats sleep 15 hours a day while dogs and cats sleep more than 8 hours... while elephants sleep only 4 hours.. I read there a direct correlation between the need for sleeps and size of animals.. something to do with metabolism.. the bigger an animal, the smaller its metabolism... so less sleep.. but what has sleep got to do with mitochondria of the entire organism.. not just the brain? unless for those who believes it benefits the brain only, please explain the above observations like correlations of size of animals and sleeping requirements.

Is that really true? Felines come in a wide variety of sizes and all of them sleep as much as they can.

A lot of doctors now say that people should sleep 9 hours a day instead of 8, and that's around how long Sloths spend sleeping!

I found this on wikipedia: Comparative average sleep periods for various mammals (in captivity) over 24 hours

horses - 2.9 hours
elephants – 3+ hours
cows - 4.0 hours
giraffes - 4.5 hours
humans - 8.0 hours
rabbits - 8.4 hours
chimpanzees - 9.7 hours
red foxes - 9.8 hours
dogs - 10.1 hours
house mice - 12.5 hours
cats - 12.5 hours
lions - 13.5 hours
platypuses - 14 hours
chipmunks - 15 hours
giant armadillos - 18.1 hours
little brown bats - 19.9 hoursI think this kind of disproves what you said. Lions are bigger than cats but sleep more, rabbits are smaller than humans but sleep about the same amount, elephants and horses are completely different sizes but sleep around the same amount of time. (just a little terminology note: if it was right I don't think it would be a "direct correlation" because it would be a negative correlation. (One variable goes up, one goes down))

Wikipedia suggests it has more to do with the eating habits of the animal than its size, as well as the amount of predation it has to worry about. If you're on the top of the food chain you can sleep more. If you have to eat almost all day to get enough food to survive you can't sleep much. I guess usually being big means having to eat more, but not if you're predator. http://en.wikipedia.org/wiki/Sleep_(non-human)#Sleep_in_different_species < loooooooooove that cat

 

[rodsika]

I am insomniac... i have to take ambien (zolpidem), a sleeping pill.. just to sleep and I only sleep 4 hours a day. When I sleep 2 hours.. I can feel my body heating up in the day.. that is why I think part of the reason for sleep is to either add heat to the body or to make the ATP synthesis more efficient in the entire body.. not just the brain. But why and how exactly? That is the question.

 

[RabbitWho]

They said in the Berkeley lecture that a lot of insomniacs actually technically get 8 hours of sleep a night, though they're obviously not aware of it and usually exhausted anyway.

They didn't give any details of the experiment. I wonder what they actually meant, maybe the brain takes quick 10 second opportunities to slip into REM.

There was a radio DJ who used to hold the record for the longest period of time spent without sleep (he did it on purpose), something like 10 days, I forget, in the end he was hallucinating and he thought the doctors were trying to kill him. When they tested his brain they found even though he seemed to be awake the readouts were identical to those of a sleeping person. So it seems even though he was conscious in most senses the brain was somehow getting the types of sleep it needed. Maybe the brains of insomniacs do something similar?

I don't know nothing 'bout no ATP synthesis

 

[Drakkith]

I am insomniac... i have to take ambien (zolpidem), a sleeping pill.. just to sleep and I only sleep 4 hours a day. When I sleep 2 hours.. I can feel my body heating up in the day.. that is why I think part of the reason for sleep is to either add heat to the body or to make the ATP synthesis more efficient in the entire body.. not just the brain. But why and how exactly? That is the question.

I don't think this is true. I think that your temperature regulation is slightly off due to lack of sleep or something similar.

 

[rodsika]

I don't think this is true. I think that your temperature regulation is slightly off due to lack of sleep or something similar.

I wonder if anyone else encounters this. When I lack sleep or too tired. I can feel my testicles getting hot. I think the explanation is the blood in the legs flow faster that is why there is feeling of heat to the body. Now why does the blood in the body flow faster? It's because there may be lack of heat in the cells for lack of sleep. So the body compensates by making more blood flow. Also isn't mitochrondrial processes of ATP synthesis partly contribute to the body ambient heat, first agree with this portion and why not if not?

 

[Pythagorean]

The body doesn't actually need sleep, it's the brain that needs it. And yet the brain is very active when we sleep.

Oops, I didn't catch this, didn't see anybody else comment on it yet. This isn't true. The body needs sleep. In fact, rats, when forced to stay up, developed open sores that would not heal and their hair started falling out. Even in humans, a significant portion of wound healing depends on sleep.

Of course, the brain has important house-keeping during sleep cycles, too. There is a large amount of transcription and cellular trafficking that occurs when light cues disappear, particularly pertaining to proteins like fabp7 and psd9, important forming and regulating synaptic junctions.