
Why Do We Sleep? - fogus
http://neuroskeptic.blogspot.com/2009/09/why-do-we-sleep.html
======
scotty79
Dolphins do sleep. But only with half of the brain.

One of the functions of sleep might be just inactivity but another much more
important one must be associated with neurons.

I think sleep (namely REM phase) is needed for neural network to avoid
overlearning. That's why sleep deprived persons hallucinate. Their neural
network is overlearned to recognize stimuli from senses and it recognizes
known patterns even if stimuli is week. Nothing better to avoid that is to
disconnect neural network from muscles (to avoid hurting yourself) and
discharge neurons randomly for some time.

------
damienkatz
Like any long running system, it's the pause while the garbage gets collected
and data is rearranged for more efficient access.

The animals that "never" sleep are actually just failing-over to the other
processor while the GC happens.

------
SamAtt
I could be over simplifying but this theory doesn't seem to stand up to basic
scrutiny.

If Siegel's theory were true than people wouldn't die from lack of sleep. At
least, not if they were given enough energy to sustain themselves without
going dormant. But that doesn't work, people do die from lack of sleep. So how
can someone make the argument that sleep isn't serving some vital purpose?

~~~
jerf
I think the place the article here goes wrong is "This theory stands in
contrast to the idea that sleep has a restorative function...". I don't know
if the original proponent is claiming this, as I find the post can be read
either way.

Basic evolutionary theory would point out that even if sleep _started_ out as
a totally optional thing that could be skipped with no loss, that evolution
would rapidly start using the sleep period as a hook to load in other things
that provided an adaptive advantage. For instance, as long as you're going to
be sitting there doing little-to-nothing in a controlled, predictable manner,
why _not_ load all your muscle repair into that time period, leaving your
wakefulness period with muscles _not_ concerned about repair? Why _not_ load
various cognitive batch processes into the sleep period, as long as it is
there, leaving you with a brain that isn't worried about those things during
the wakefulness period and therefore spending more energy on useful
computation, or even just plain spending less?

I've actually directly observed this process in my evolutionary computation
homework assignments. I choose that phrasing to indicate my not-extensive
experience on the topic, and that even so, I've seen this, where chunks of
useful code get loaded up with other stuff that bears some sort of
relationship to the original. (And evolution has a strange idea of
"relationship".) (I do sometimes think that evolutionary computation should be
a required course for biologist PhDs; the hands-on experience is invaluable.)

I often wonder at "either/or" arguments in the context of evolution; to me it
betrays a profound misunderstanding about the process. It is the very
incarnation of a "both/and" process. Is sleep an optional resting period just
to conserve energy, or a time for healing, recovery, and cognitive batch
processes? Perhaps there was a brief time when the answer was one or the
other, but today the answer is simply "Yes", in general. (Your Species'
Mileage May Vary, I'm speaking to the general case.)

~~~
silvestrov
I agree. In the (pre)stone age, it was very dangerous to wander around in the
night. So humans (and other such animals) that could keep still at night were
at an competitive advantage. Sleeping is the ultimate keeping still. And
evolution just improved on that, using the sleep for other stuff, which then
became unskipable.

It seems for me that many of those who accept evolution, still thinks in
creationist terms: that however the human body works today, must have been the
original purpose. And that we are not the result of an evolutionary history
filled with random input and short-sighted adjustments, thus ending up with
something that could never have been conceived in the beginning.

Sometimes stuff "just came into existance" without an (initial) purpose.
Purpose is not a pre-condition for existence.

------
fburnaby
What about drowsiness? If sleep is just a behavior for keeping us out of
harm's way, shouldn't we be able to just "switch back on" upon being awaken?
Granted, sometimes we do just start awake. But still, staying out of harm's
way and resting sounds like a good reason to develop _patience_ , but sleep.

Are there many species that sleep with their eyes and ears open?

