From: mcgrath@cs.uiuc.edu (Robert McGrath)
Subject: Re: Near Death Experiences
Reply-To: mcgrath@cs.uiuc.edu
Organization: University of Illinois, Dept of Computer Science
Date: Fri, 16 Oct 1992 17:55:04 GMT

In article <1992Oct16.073951.16583@news.ysu.edu>, ae553@yfn.ysu.edu (David Jameson) writes in part:
|> >
|> >I also claimed that brain activity can continue for at least a while 
|> >with oxygen cut off.  This is clearly possible, as it happens all the 
|> >time when people are resucitated from heart failure.  Naturally, there 
|> >may be damage, and the experience may be wierd....
|> >
|> You seem to have missed the point of my question.  You simply stated
|> that the brain can survive without oxygen for a limited time, but I
|> was asking whether the brain can actually function without a supply
|> of blood (something totally different).
Sorry, I missed this detail of you comment.  Substitute lack of blood
for lack of oxygen and I think what I said is still OK.

|> It is possible for neurons to survive for between about three and ten
|> minutes after the blood supply has been shut off, but just because they
|> haven't died doesn't necessarily mean they can still function.
|> For a neuron to operate there needs to be an energy supply in the form of
|> glucose, which is supplied by the blood.  Cut off the blood supply and you
|> deprive the neurons of the energy necessary to transmit signals.  The only
|> way neurons could possible operate in this situation would be if they
|> stored large amounts of glucose somewhere.
Which gives you about 10 minutes or so, give or take a bit for metabolic
differences (maybe high levels of glucose in the blood, or metablolism
tuned real low) and the possibility of variability among cells (i.e., some
live longer than others).  Is this drastically different than what
I said?

|> Consider, for example, a person fainting.  For some reason or another, the
|> brain isn't getting enough oxygen and the person gradually begins to lose
|> consciousness.  First there is a loss of sound and then a loss of vision,
|> followed by loss of consciousness if the situation continues.  When the
|> person recuperates there is no brain damage, but while the person was
|> unconscious certain parts of the brain were unable to function because
|> of lack of oxygen.  If not (i.e. if the brain can continue to function,
|> as you seem to be implying), why did the person lose consciousness in the
|> first place?

You seem to be equating consciousness with brain activity.  Even when 
unconscious there is plenty of activity, although the person is not 
aware of it.  As far as I know, once all brain activity stops, it can never 
be restarted, so any time someone revives there was at least a little 
brain activity still going.  (This is the basis of my comments about
how long brain activity can go on--people have been revived after
amazingly long times without oxygen, from which I infer that at
least a litte activity continued.)

The hypothesis is that in some cases, some of this activity is picking
up some information from the senses, although it is not noticed or
consciously at the time.

-- 
  Robert E. McGrath
  Urbana Illinois
  mcgrath@cs.uiuc.edu