From: Eugene Leitl (Eugene.Leitl@lrz.uni-muenchen.de)
Date: Mon Jul 28 1997 - 18:08:28 MDT
---------- Forwarded message ----------
Date: Mon, 28 Jul 1997 16:39:32 +0100
From: aray_@emory.edu
To: "bionet.neuroscience mail newsgroup" <bionet-news@dl.ac.uk>
Subject: Re: dreaming reality: the neural servo
While your theory is interesting, your "observations" on sleep are
somewhat incorrect. People don't "go back to their early childhood"
during deep sleep. Assuming for the moment that you mean that people go
back during dreams, there is very little dreaming during deep sleep
(Stage 3/4). Most dreaming is during REM sleep, and the brain is
relatively aroused during REM. In fact, the brain is fully "awake" in
many senses - it actively suppresses motor function while you dream (and
greatly raises the sensory threshold so most sensory input is blocked
out). A majority of dreams are reported to be a mixture of very recent
(the past day or so) memories and associations between those memories
and slightly older memories (sometimes very bizarre associations). A
very small proportion of dreams involves distant memories, such as early
childhood memories.
Some other sleep-related comments: True, the cortical oscillations
are slow and of high amplitude. But sleep depth doesn't "shut down" the
less "primitive" parts of our brain: Those oscillations are from
cortical cells firing in unison, most likely due to thalamic neurons
controlling the pattern of cortical firing. All these parts of our
brain are still active - they still function. Furthermore, these parts
of our brain are still functional in childhood - our brains are almost
completely developed by childhood. True, not all the connections are
complete, but many are.
People cycle through sleep stages several times in the night. We
don't just get into a deeper sleep as the night progresses, it gets deep
then shallow, even occasionally waking up before drifting back into the
deeper stages again. And then, of course, there's REM sleep, which is
electrically (EEG) nearly identical to awake brain activity. Any
signals we pick up tend to be incorporated into our dreams (REM sleep),
when the threshold for sensory input is lower (i.e. more input can
occur). During stage 3/4 sleep, the threshold for sensory input is
extremely high, so only something as strong as a loud alarm or other
noise will be registered by the brain. Weaker stimuli don't get past
the auditory/visual nerves. We don't wake up in the mornings because of
increased sensory input (the "supply of reality") - just ask anybody
that works a third shift or parties all night. The need for sleep can
temporarily override circadian rhythms, and easily override sensory
input - that's why people who work those shifts can sleep til 1300 (1
PM) and stay awake until 0500. Of course, circadian rhythms can take
precedence - thus the ability to nap in midafternoon, when your
circadian rhythm is naturally "low". No one is sure what initiates the
transition from sleep to wake, or vice versa, but input from thermally
sensitive neurons, and the brain's balance between acetylcholine and
monoamine neuroactivity, have both been implicated. The idea that the
brain corrects "reality" is interesting, and one I've heard of before,
but I still have the same question - if the brain is involved in fixing
reality, why can someone be killed without getting the sensory input
that says he is going to die? That is, the external reality of sleeping
in the wild (or on train tracks, etc.) can intrude on the person without
the brain ever knowing - the brain and body will then stop functioning.
Presumably, reality shouldn't change or change much if the brain is
controlling reality and not just our perceptions of it. In other words,
how can external things intrude on your body if it is your brain which
makes reality? Even if you were conscious, and assumed that your brain
intuitively knew physics well enough for a bullet to kill you, if you
closed your eyes before you saw the shooter you wouldn't know the bullet
was fired at you and you shouldn't get hit by it - unless you have a
death wish. And when you're asleep, there's no sensory input, so how
can a bullet even hit you when it shouldn't exist?
Lack of sleep does not have the same effect as panic. You can get
hallucinations (not generally a symptom of panic but sometimes a cause)
with long sleep deprivation. More often though, slight confusion and
the ability to fall asleep much more easily are the main neural
manifestations. Our bodies slow down slightly, whereas in panic our
sympathetic nervous system is in overdrive. Again, refer to the
question above in regard to creating reality from within.
Just my 2 cents...
Andrew Ray
aray_at_emory.edu
To reply to my address, replace the _at_ with @.
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