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From: rowe@pender.ee.upenn.edu (Mickey Rowe)
Newsgroups: sci.bio
Subject: Re: Echidnas & REM sleep
Message-ID: <42217@netnews.upenn.edu>
Date: 29 Apr 91 18:26:24 GMT
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In article <619614w163w@shark.cs.fau.edu> tomh.bbs@shark.cs.fau.edu 
    (Tom Holroyd) writes:

>I'd say that, in the absense of input, the natural state of the cortex
>is low activity, synchronized.

Hmmmmmm...  In the first place I'd doubt that sleep represents an
absence of input...  Just because you don't remember the sensory
experiences that you have when you're asleep doesn't mean that they're
not there.  I live in a city near busy streets, and I assure you that
my ears are getting plenty of stimulation regardless of my conscious
state.  It seems to me that input is not absent, it's just ignored.  

In the second place, I'm not so sure that I would agree with this
natural state.  Perhaps you could make a case for this from the
cerveaux isole or encephale isole studies, but I wouldn't put much
credence in it if you didn't have other evidence.  You might also want
to look at Ron Harris-Warwick's stuff about modulation of oscillatory
circuits.  Assuming that the periodic activity in EEG's comes from
cyclic activity amongst groups of neurons, his work could be relevant.
He's studying the stomatogastric ganglion of crustaceans, and showing
that this single network of about six types of cells has vastly
different properties depending on what types of neurotransmitters he
puts on them.  Which cells are active, what the phase relationships
are between different types of cells etc. changes pretty dramatically
with small concentrations of neurotransmitters.  I would tend to argue
that there is no "natural" state of a group of neurons...

>  The cortex needs input to desynchronize it.
>There is reduced input during sleep, hence more oscillatory behavior.

My feeling is that your causality here is completely uncalled for.  In
fact Charlie Gray's work indicates that visual input causes oscillatory
behaviour in area V1, and that oscillatory behavior as a response to
input may be the manner in which different attributes of a single
stimulus are grouped together.  Granted these oscillations are much
faster than theta waves...

>From what I've read, it's difficult to get sleep researchers to
>agree. :-)

Oh, I'm sure that half of them would disagree with that :^)

>I'm speaking from the point of view of dynamical systems.  If the cortex
>remains in a limit cycle state for too long, it may be difficult for
>it to escape.  

I'm afraid that I don't completely understand your terminology, but I
guess that the missing piece for me here is an implied suggestion that
the purpose of sleep is to put cortex into this limit cycle state.
What would the advantage of that be?  (This is a real question, not a
challenge.) 

>I have gotten a response from someone who said there was only one
>experiment done to show that echidnas have no REM sleep, and the
>animal may have been hibernating, not sleeping!  This brings up
>the question of whether hibernating animals in general have REM
>sleep or not.  I don't know.

If they don't I think that your idea about why REMS exists is on
pretty shaky ground...

>Tom Holroyd
>Center for Complex Systems
>Florida Atlantic University
>tomh@bambi.ccs.fau.edu

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