Why do we sleep?

Robert Bradbury rbradbur at u.washington.edu
Sat Mar 19 21:51:14 EST 1994

All of the information I have seen indicates that respiration decreases
and temperature drops during sleep.  There may be exceptions to the
temperature drop if you have a genome which is biased towards burning
excess calories and consume lots of calories before going to sleep.

One consequence of these changes is that you will greatly reduce the damage
which occurs to DNA (70,000+ base hits per cell per day) due to reduced
production of free radicals and less spontaneous depurination/depyrimidation
which is temperature related.  Sleep in "higher" animals usually occurs
in conditions which are relatively safe and a period of down-time may
allow maintenance and repair processes to take place which could be
potentially harmful if they occured during hours when threatening
conditions could arise.  So during sleep you may get increased levels
of hormones (growth hormone and melatonin come to mind) which may direct
restructuring of tissue and/or repair processes.  In looking at this
a key fact to think about is the wiring from the visual cortex to the
pineal gland that causes melatonin production to be curtailed when
your eyes detect bright light.

In line with this "higher" animals have memory systems which are designed
to perform extremely rapid analysis of threatening situations (e.g. the
fight or flight response).  This requires that we have stored information
for "threatening" situations in such a way that allows rapid comparison
with our current environment to determine the proper response.  It may
be that the structure of the brain does not allow real-time processing
of environmental information into storage structures for fast future
reference.  So we save the information in temporary storage during
the day and while we are asleep process it into the information network
for future reference.  This would be interesting in view of the Dolphin's
half-on/half-off solution.  Since dangerous conditions might arise at any
time so you don't ever want to turn off all of your awareness/comparison
computer.  It would be interesting to study the sleep requirements in
relation to the memory capacity and complexity requirements of an
organism's friend vs. foe analysis.  Do sleep requirements increase
with the size of the memory and with animals whose "friends" may
one day turn out to be "foes"?  Do they decrease in species where
animals run as packs where some animals always serve as "guards"?

Robert Bradbury					bradbury at aeiveos.wa.com

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