
What is the real reason we sleep? - sfled
http://www.bbc.com/earth/story/20160317-what-is-the-real-reason-we-sleep
======
pizza
Very relevant PubMed article many of you will undoubtedly find interesting:
"Partial sleep in the context of augmentation of brain function."

Abstract: Inability to solve complex problems or errors in decision making is
often attributed to poor brain processing, and raises the issue of brain
augmentation. Investigation of neuronal activity in the cerebral cortex in the
sleep-wake cycle offers insights into the mechanisms underlying the reduction
in mental abilities for complex problem solving. Some cortical areas may
transit into a sleep state while an organism is still awake. Such local sleep
would reduce behavioral ability in the tasks for which the sleeping areas are
crucial. The studies of this phenomenon have indicated that local sleep
develops in high order cortical areas. This is why complex problem solving is
mostly affected by local sleep, and prevention of local sleep might be a
potential way of augmentation of brain function. For this approach to brain
augmentation not to entail negative consequences for the organism, it is
necessary to understand the functional role of sleep. Our studies have given
an unexpected answer to this question. It was shown that cortical areas that
process signals from extero- and proprioreceptors during wakefulness, switch
to the processing of interoceptive information during sleep. It became clear
that during sleep all "computational power" of the brain is directed to the
restoration of the vital functions of internal organs. These results explain
the logic behind the initiation of total and local sleep. Indeed, a mismatch
between the current parameters of any visceral system and the genetically
determined normal range would provide the feeling of tiredness, or sleep
pressure. If an environmental situation allows falling asleep, the organism
would transit to a normal total sleep in all cortical areas. However, if it is
impossible to go to sleep immediately, partial sleep may develop in some
cortical areas in the still behaviorally awake organism. This local sleep may
reduce both the "intellectual power" and the restorative function of sleep for
visceral organs.

[https://www.ncbi.nlm.nih.gov/pubmed/24822040](https://www.ncbi.nlm.nih.gov/pubmed/24822040)

------
yason
What if the question was phrased as what is the real reason we wake up and
dedicate some conscious time for our mind? Surely, because in the physical
world we live we need to arrange for some time to deal with the unavoidable
practical things such as finding food and shelter. Then, after a long enough
period of this activity focused on these very tangible, physical and
physiological constraints we can finally say we _fall to_ sleep again.

~~~
KannO
We can't all be plants and fungus.

~~~
Majestic121
Why?

I think it is possible for life to evolve on a planet with only plants and
fungus.

Plants have been pretty successful down here on Earth, and I think most of
them don't need animals for their survival (except flowers?).

~~~
ComputerGuru
Flowers don't necessarily need animal life either, though it does help. Wind
can pollinate.

~~~
saalweachter
More importantly, plants evolved in the context of animals; if animals didn't
exist, plants wouldn't have evolved seed dispersal or pollination strategies
relying on them. They might have even evolved strategies we've never seen,
that don't work well when there are animals running around eating everything.

------
narsil
I took Matt Walker's class on sleep at UC Berkeley (Psych 133) and it was
fascinating. Short-term effects of a lack of sleep are easily observable, and
I'm sure we can all relate from personal experience. However, long-term
effects of sleep deprivation are harder to determine. One of the few known
correlations appears to be that people who are susceptible to psychiatric
disorders such as schizophrenia are more likely to experience them as they
age, if they suffer from chronic sleep deprivation.

"Sleep problems may increase risk for developing particular mental illnesses,
as well as result from such disorders." \-
[http://www.health.harvard.edu/newsletter_article/Sleep-
and-m...](http://www.health.harvard.edu/newsletter_article/Sleep-and-mental-
health) (2009)

~~~
ctolsen
This is an interesting one. I have sleep apnea, the result of which is
basically chronic sleep deprivation even though you spend lots of time in bed.
I struggled with all sorts of depressive symptoms (depression, anxiety, panic
attacks) for years before getting a diagnosis, and 90% of the symptoms
vanished overnight after treatment.

------
AndyNemmity
I tend to believe it's tied quite closely to memory and emotional states. I
had very bad sleep apnea that was untreated, and for the time that it was
untreated my memories are extremely vague compared to most.

I also had very high anxiety which is completely gone now. Now that I use a
machine to sleep my memory is sharp again.

I also eat much less now, so I believe that calories were a way the body would
attempt to counter act the lack of rest.

These are just my thoughts, I honestly don't have any scientific background on
it. Just my own experiences.

~~~
lamby
How did you discover you had sleep apnea?

~~~
Hydraulix989
Probably through an overnight clinical sleep study.

~~~
fredrik-j
Another option is to perform a sleep study at home. You borrow a wearable
device that records your sleep quality, breath, ECG, etc. You wear it over
night, then turn it in for analysis.

Common symptoms of sleep apnea are if you're regularly tired without apparent
reason or experience a reduced ability to concentrate during daytime, or if
your surrounding complains that you snore loudly.

~~~
Hydraulix989
Careful though, as HST can under-report events, resulting in a lower AHI score
than if you got the clinical PSG.

------
plinkodemayo
All of these answers for why we sleep - garbage collection in brain processes,
energy recovery - beg the question, why do these processes HAVE to happen
during sleep, instead of during wakefulness.

I suspect that it's an artifact of the Earth having a day-night cycle at all.
Imagine the very first organisms on earth. One is always wakeful, and spends
all of its awake time hunting for food. During the earth's night cycle,
hunting for food is harder - it's colder, so smell molecules travel more
slowly. It's darker, so you can't see food as well. The organism has to work
harder to gain the same calories compared to during the day. If there's
another organism that goes into a low-energy state during the night, it
exchanges the risk of being killed for food during the night with the lower
energy budget of not needing to be active at night. Even if a particular
organism gets eaten, it's a net positive for the species, and these organisms
can outcompete the wakeful organisms.

Then, as sleepfulness becomes part of the successful energy budget of early
organisms, you can further optimise nighttime activities - organisms that do
brain garbage collecting during the night can do so more efficiently than
organisms that also sleep but do continuous garbage collecting. Because sleep
was the optimal strategy for primitive organisms, fitting recovery into sleep
becomes selectively chosen for.

The only way to prove this, though, would to find a planet that has no
day/night cycle, and see if those organisms have any sleep behavior.

~~~
gizmo686
>The only way to prove this, though, would to find a planet that has no
day/night cycle, and see if those organisms have any sleep behavior.

Deep sea hydrothermal vents provide this experiment on Earth. While the
ecosystems are not completely isolated from our sun based ones, they are
pretty insolated from it. Of course, to actually prove this you would need
multiple, independent, evolutions of life with a day/night cycle and multiple
evolutions without one.

~~~
plinkodemayo
It might happen.

------
jklp
I remember watching this TED talk a couple years ago which stuck with me,
though am not 100% sure on its validity.

[http://www.ted.com/talks/jeff_iliff_one_more_reason_to_get_a...](http://www.ted.com/talks/jeff_iliff_one_more_reason_to_get_a_good_night_s_sleep#t-242971)

The theory being that sleep was a way to clear out waste from the brain during
normal operation, due to the lymphatic system not extending to the brain, it
has to put itself into "sleep mode" to drain the waste.

This might explain why memory is usually better after a good night's sleep,
and also the cause of dreams - which is just misfiring of neurons while the
waste is being cleared.

~~~
fian
So sleep is something like garbage collection in Java? Some
perceptions/thoughts you experience during the day need to be mived from a
finite sized young generational heap to a long kived heap (ie convert
important short term memories to long term memories). This then frees uo space
in the young gen. heap for the next day. Dreams could potentially be the
result of a reference check being performed to see which memories to move to a
different heap and which can be discarded.

------
carsongross
Conjecture (half serious): we won't get strong AI until we figure out why we
need to sleep.

~~~
gregatragenet3
Probably related. Mammals dream, and we humans experience time in dreams much
faster than the actual passage of time. Dreaming is likely the same mechanism
as 'experience replay' used in AI reinforcement learning. We're just training
our neutral networks using minibatches of our experiences from our waking
hours.

~~~
argonaut
"Likely" is not the word I would go for. "according to my wild guess" is a
more accurate term.

~~~
matt4077
I've heard it before and it's not their wild guess but a seriously discussed
idea. It's just that it's hard to set up experiments to test these sort of
ideas.

~~~
oldmanjay
It can be a seriously discussed wild guess. It's not like there's some
dichotomy to be satisfied there.

------
vacri
Two things missing from the article: physical repair is improved in sleep; and
the laydown of long-term memories is an important part of sleep. You can screw
up someone's memory of the previous day by waking them at the right times.

And, as usual, REM sleep steals the show. Probably because of that funky
acronym, and that's when we tend to have movie-like dreams. Wake people up at
the right time in slow-wave sleep and they'll report 'dreams' that are just
sounds or flashes of light.

Bonus factoid: you can wake most people up from even deep sleep by calling
their name a few times. When I was a 'sleep technician', that's how I used to
wake people up when I had to fix a sensor - much more gentle than physically
touching or shaking them.

It's a bit disappointing that journalists are still peddling the "sleep is a
great big mystery" angle. And also that the article is arguing that there must
be _one_ particular reason why we sleep. There isn't one reason why we
respirate, one reason why we digest, or one reason why we circulate - why
should there be one reason why we sleep?

~~~
tremon
In my mind, all of your other examples have a singular answer, even if the
answer isn't the full story.

 _one reason why we respirate_

To replenish the oxygen in our blood.

 _one reason why we digest_

To extract energy from our food.

 _one reason why we circulate_

To distribute nutrients around the body.

Simplified as those answers may be, they're not wrong FAFAIK, they're
incomplete. Do we have such a single not-completely-wrong answer for why we
sleep?

~~~
vacri
Well, the one thing you've missed in all the items is waste removal, which is
just as important as nutrient distribution. Also, we absorb more from our food
than just energy. And even then, you caveat your answers with "but these are
simplified and incomplete".

Then compare to the article, a bit of long-form journalism rather than throw-
away summary lines, which opens with the statement that there's one crucial
reason for sleep and we don't know it.

------
LouisSayers
One thought I've had recently: What if being "unconscious" isn't unconscious
at all - what if it's a different form of consciousness?

For instance, it deals with the internal world of our body, maintaining and
dealing with issues as they happen. It's responsible for releasing chemicals
to get a desirable action from our 'conscious' self. It gives us rashes in an
attempt to change its environment.

I haven't thought about this too much, but in the very least, I think it's an
interesting thought experiment. Has anyone actually tested that our
'unconscious' is indeed unconscious?

------
NoMoreNicksLeft
Bad legacy firmware, same answer as always.

------
noiv
I like the idea of sleep as a consequence of information processing. At some
point an organism needs to get rid of useless information acquired by its
sensors previously. That's also why Maxwell's demon can't brake the second law
of thermodynamics. Looking at people's behavior suffering sleep deprivation
'information overload' comes easily to mind. Perhaps the ability of REM sleep
is a sign of some form of consciousness, which in turn is just an efficient
way to process information and detect the useful bits.

------
netman21
This rambling summary article touches briefly on "natural selection" but no
one has yet to look into what seems obvious. In mammals where most parents
have to care for their young, if the young did not sleep, did not give their
parents a break for long periods, they would not survive. Therefore sleep is
selected for. Those offspring that sleep survive, passing on the sleep trait,
to their offspring. - Source: parent.

~~~
agentgt
While I agree that sounds like a plausible theory (and sort of reminds of the
domestication theory... ie cute animals get more parental and human focus) but
there are just too many animals that barely take care of their young that
still sleep.... for example sharks sleep.

~~~
erroneousfunk
Also, why would we keep on sleeping into adulthood if it was such a massive
risk and waste of resources? It doesn't make sense that adults also sleep when
they're "getting a break from their kids"

------
mchahn
> forcibly keep an animal awake for long enough and you will kill it. The same
> almost certainly applies to humans.

There was a PBS Nova episode on sleep many years ago. It showed people who
never sleep. They are rare but they exist and have been studied extensively.
They do have down-time where they rest for hours, but they never fall asleep.
If this was any other show than Nova I'd call bullshit.

~~~
jjoonathan
You're sure they weren't talking about people on polyphasic sleep schedules?

Also, fatal familial insomnia is a thing, so we have a pretty good idea of
what happens when people are deprived of sleep for too long.

~~~
poizan42
FFI is a bad model for long term sleep deprivation since massive neuronal loss
is also involved.

~~~
tremon
Just asking: do we know that massive neuronal loss does not occur with
"normal" long term sleep deprivation?

------
amelius
A related question: why do some (actually a lot of) people grind their teeth
during sleep?

According to wikipedia: The ICSD-R states that 85–90% of the general
population grind their teeth to a degree at some point during their life,
although only 5% will develop a clinical condition.

~~~
swsieber
I'm not sure, but anecdotally, one person I know said that it had been an
issue, until he started limiting how much liquid he drank starting 3-4 hrs
before bed.

------
kazinator
Not just

Of course, we sleep because we evolved from other forms that already slept!

The understanding of sleep isn't complete without taking into account why
animals sleep.

Sleep could have gotten more complicated during evolution; acquiring new
functions.

------
pessimizer
Running repeated passes of lossy compression.

------
EA
My guess: predators hunt at night. The quieter you are, the more likely you
are to survive another night.

~~~
tremon
Our ancestors (primal mammals) were nocturnal. They slept during the day.

------
TianHua
I never think about this question, now I am thinking it, but the question may
be that I cannot think it all the time without doing anything else, Ok, let's
go to sleep for some rest.

------
eximius
"Because we get tired." is what I've always heard from people that aren't
researching it.

~~~
insulanian
Define _tired_.

------
dschiptsov
Maintenance.

~~~
pluma
Apt, but doesn't that describe most of what our bodies does even when we're
awake?

------
meshr
I have another idea why we sleep: the reason lays in physics, it happens
because the sun is not shining all the day. So the living creatures had to
create a mechanism to be more active while daylight. That is why all “garbage
collection” activities were moved from daylight activity to the night.

