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In article <BzsJHL.J31@iat.holonet.net> ken@iat.holonet.net
     (Ken Easlon) writes:

>In article <BzF4sA.Jyx@dcs.glasgow.ac.uk> ,
>jack@dcs.glasgow.ac.uk (Jack Campin) writes:
>
>>geb@cs.pitt.edu (Gordon Banks) wrote: 
>>> RGINZBERG@eagle.wesleyan.edu (Ruth Ginzberg) writes: 
>>>> Does anyone know what causes the sensation (when just falling asleep) 
>>>> of sudden literal falling, followed by a startle reaction that wakes 
>>>> you right up? 
>>
>>what the heck is it FOR?  

I can't answer your specific question...

>>Anything this widespread ought to have some 
>>physiological function and evolutionary rationale, surely? 

...however I will caution you against the "rabid selectionist"
viewpoint.  We (humans) seem to have a tendency to assign "purpose" to
anything and everything.  Up until the mid-late 1800's scientists
thought of this "purpose" as God's plan.  In biology, that viewpoint
was largely overturned by Darwin (note that I'm *not* saying that
evolution does away with the concept of God, only that our current
framework for wondering why zebras have stripes, or why oysters make
pearls or whatever are very different from pre-Darwinian viewpoints).
Although our perspective has changed, our psychology has not.  We
still want to assign "purpose" to everything.  Now instead of "God
made it that way", people reflexively say "it was adapted to be that
way".  That response is probably as often wrong as right.  

The startle response which often occurs when you're falling asleep may
well be an artifact with no adaptive significance whatsoever.  I don't
want to make the case that this is so, but I do feel that:

>>Anything this widespread ought to have some 
>>physiological function and evolutionary rationale, surely? 

is worded much too strongly.

On to another response...

>I think it's associated with the disconnection of gravity sensors in the
>sleep state.

I'm kind of curious as to what you're talking about here.  During REM
sleep (when most dreams occur), there is an active inhibition of your
motor neurons, but I don't know of any special "disconnection of
gravity sensors".  Do you?  

>This is offered from a strictly subjective point of view, and may not have
>any neuro-biological basis, but when I'm asleep I tend to maintain a
>certain amount of body awareness.  For example, if I'm sleeping on my side
>with one knee cocked, I am more likely to have dreams about climbing stairs
>or some similar activity requiring the same body position.

I'm really curious as to how you have tested this.  I actually suspect
that it is false, but am open to suggestion.  I think that the only
way that you could make the above statement meaningful would be if you
had somebody else watching you sleep, noting your body positions, and
waking you in the middle of your REM episodes.  A comparison of your
body positions and your dream content would then be meaningful.  I
*really* don't think that you could perform any sort of similar test
on your own.

>I suspect this gravity disconnect is necessary for dreaming about activity,
>otherwise we'd probably only have dreams of lying down.

I also think this is a bit of nonsense.  You're presupposing that
outer events (e.g. body positions) play a strong role in your dream
content.  While I'm sure that we've all had the experience of
incorporating annoying sounds into our dreams as we sleep through our
alarm clocks, there doesn't seem to be such a clear connection between
our contemporaneous outer reality and the inner reality of our dreams.
If you want to find out more about current neurophysiological
conceptions on the origin of dreams I recommend _The Dreaming Brain_,
by J. Allan Hobson, Basic Books, New York, 1988.

>Ken Easlon                | "...somebody spoke and I went into a dream..."

Mickey Rowe     (rowe@pender.ee.upenn.edu)