Zzzzzzzz We have to do it every night but nobody knows why
gwhelan at access.net.au
Mon Sep 27 06:36:22 EST 1999
It's not that we don't know why we sleep, it's just that it is difficult to
The slow wave sleep (SWS) referred to is the time that growth hormone is
released at twice the normal rate and also the period during which
neurotransmitters are synthesized in the brain at up to four times the rate done
at any other time. Ever wonder why we get a little fuzzy in our thinking when
sleep deprived, have trouble with judgement and with co-ordination? The immune
system also gets a boost while we are experiencing SWS.
The rapid eye movement (REM) sleep appears to have very little to do with
consolidation of experience and more to do with establishing and repairing
connections in the brain. A foetus at 26 weeks gestation spends 100% of its
time in REM sleep, having had almost no 'experiences' to deal with and no
psychological dilemmas which Freud proposed as the function of dreaming. A
new-born baby spends 10 of its 20 sleeping hours a day in REM sleep, this amount
diminishing as the brain approaches its adult size.
Total sleep deprivation will kill. There is a point of no return marked by
hypothermia after which a person will die, no matter what sleep they are allowed
and what care they are given after that point. This is the result of a poorly
functioning immune system. True, the cause of these deaths was a mystery for
many years, but it has been shown to be septicaemia. The mammals tested min
these experiments were simply overwhelmed by the sheer number of bacteria in
their bodies, hence the increasing energy consumption but decreasing weight and
body temperature. Very difficult to detect when the responsible organisms are
those that ordinarily inhabit the body and are totally benign. It just goes to
show you won't see what you're not looking for.
I was disappointed to see that the article below was from New Scientist. I
would have expected more thorough research from such a journal. Clearly they
needed a filler piece in a hurry and thought that naming a few related
disciplines and calling on the name of evolution - which we should remember is
still a theory, not a fact - would create something to pass for a credible
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> We have to do it every night but nobody knows why
> AT THE END OF A CENTURY when the mysteries of life have fallen one after
> another to the advance of molecular biology, it is reassuring to find that
> we still have one big puzzle for the next century's scientists to get their
> teeth into. Even more delightful, it's a puzzle that can be expressed in
> just four words: "Why do we sleep?"
> Nobody knows the answer, despite fifty years of intensive research. Everyone
> knows, of course, that we fall asleep because we are tired and somehow sleep
> restores our sense of wellbeing. But what exactly does sleep revive and why?
> And why can't we do without it?
> A popular view is that we sort out the day's experiences and reinforce
> memories during sleep, perhaps through a subtle transfer of information
> between different parts of the brain (see p 26). But the trouble with such
> theories is that they are both too weak and too strong. On the one hand,
> they don't explain the absolute need we have for sleep. If totally deprived
> of sleep, animals don't just become a little confused about remembering
> their way through a maze, they actually die--and almost as quickly as if
> deprived of food (see New Scientist supplement, 26 April 1997). On the other
> hand, the theories don't really explain why we can handle a few nights
> without sleep and not suffer serious mental impairment. If you don't count a
> tendency to bite everybody's head off, that is.
> Where can we look for an answer? The usual place to start when tackling big
> "what for" questions is in our own evolutionary past. Much of our physiology
> and behaviour can be understood by studying other animals, but when we turn
> to sleep the plot merely thickens.
> It is essential, of course, to distinguish between the two major phases of
> sleep--slow-wave sleep (SWS) and rapid eye movement (REM) or dreaming sleep.
> Dreaming is restricted to the higher animals-- mammals, birds and some
> reptiles--and thus seems likely to have a cognitive function. But even that
> rule has its strange exceptions. Although we might forgive the echidna, one
> of the most primitive mammals, for not indulging in REM sleep, why is it
> that dolphins and whales also seem not to dream?
> How long animals sleep is also very variable. Bats sleep for up to 20 hours
> a day. Both the giant anteater and the giant sloth also put in 18 hours, but
> the anteater dreams for around 7 hours while the sloth makes do with 70
> minutes. Is chasing ants really such a cognitive strain? Lions can sleep for
> days on end. But a shrew sleeps for only a few hours.
> Generally speaking, animals that are secure from predators sleep a lot,
> while those whose lives are at risk sleep little. That could suggest that
> sleep is designed simply to conserve energy. Evolution follows the philos-
> ophy of the couch potato--if you are well fed and secure, just take it easy.
> But even here, there are exceptions. Elephants have few predators but sleep
> little. The Indus dolphin lives in a dangerous environment but manages to
> clock up 7 hours a day.
> Perhaps all we can really be certain of is that although the amount and type
> of sleep is in some way related to lifestyle, no higher animal can survive
> without at least some sleep. Which suggests that the roots of sleep run very
> deep. Indeed, all animals go though cycles of activity and rest, even the
> humble amoeba. Sleep has always seemed to be something more complicated. But
> perhaps, after all, it is not--a view recently expressed Giulio Tononi of
> the The Neurosciences Institute in San Diego and one of the leaders in the
> field, in the question: "Can single neurons sleep?" In other words, we still
> don't really even know whether sleep is a local or a global phenomenon of
> nervous systems.
> If global, then we can expect neurobiologists to crack the problem of what
> sleep is for. If local, then molecular biologists will find the answer
> inside single cells. And if sleep is just nature's way of stopping us
> wasting precious energy then it will be behavioural ecologists who strike it
> lucky with the right theory.
> Whatever the outcome, it's good to know that we have a deep mystery left.
> From New Scientist, 25 September 1999
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