From: sfm@manduca.neurobio.arizona.edu (Stephen Matheson)
Newsgroups: talk.abortion
Subject: Re: Spoken Like a True ProLifer
Date: 12 Jan 93 18:22:14 GMT
Organization: University of Arizona UNIX Users Group

From article <1993Jan12.040001.6011@mnemosyne.cs.du.edu>,
by mcochran@nyx.cs.du.edu (Mark A. Cochran):
> In article <1993Jan11.065635.16749@organpipe.uug.arizona.edu>
> sfm@manduca.neurobio.arizona.edu (Stephen Matheson) writes:
>>From article <1993Jan10.151453.22562@mnemosyne.cs.du.edu>,
>>by mcochran@nyx.cs.du.edu (Mark A. Cochran):
>>> In article <1993Jan9.005134.29659@organpipe.uug.arizona.edu>
>>> sfm@manduca.neurobio.arizona.edu (Stephen Matheson) writes:
>>>>From article <1993Jan8.222739.20331@mnemosyne.cs.du.edu>,
>>>>by mcochran@nyx.cs.du.edu (Mark A. Cochran):

>>>>> Given that myelination is necessary for proper
>>>>> conduction of impulses in the brain

>>>>Just how "given" is this?  Before myelination, aren't most fibers
>>>>nevertheless conducting impulses, albeit much more slowly than after
>>>>myelination?  I'm going to go check this, but I'm rather sure at this
>>>>point that myelination speeds conduction rather than making it possible
>>>>(that's the job of ion channels).  Pre-myelinated fibers, in at least
>>>>some cases, are just as competent to have excitable membranes.

>>> Premylinated fibers do conduct some impulses, certainly. They are, as
>>> you pointed out, conducted at a much slower rate. They are also (if I
>>> remember my neuro) subject to transmission failure at a fairly high
>>> rate. 
>>> As an analogy, consider the conversation we are having. If every third
>>> line were dropped, or if random words were deleted, it would no longer
>>> bear any resemblance to rationality.
>>> How could we have rational thought with the same random loss of
>>> impulses?

>>I suppose if we built in enough redundancy, we might be able to pull
>>it off.

> Redundancy does not help if the signal is *lost*, although it would
> help if *multiple* signals were being sent, and only *some* were being
> lost.

That's the essence of redundancy, right?  Must I repeat myself? :-)

> Does your study or neurology indicate tha tthe brain sends out
> multiple copies of each signal? I admit I don't know one way or the
> other.

It's clear that redundancy exists in the adult brain.  This is
probably due to "multiple copies of the same signal" as well as
mechanisms that might be thought of as "error correction" (e.g.
filling in blanks).  If we assume thought and consciousness to
be emergent processes arising from complex information flow, we
can reasonably assume that the distributed nature of the network
allows for considerable redundancy in that the loss of parts of
the network does not lead to proportional loss of information.
Does such a network exist in a fetus?  More appropriately, at
what time in development is the network minimally functional?
Those are the questions.  If we better understand the network,
we can better address the question "how does myelination (or
the increased fidelity of transmission it provides) affect the
function of the network?  Is it necessary?  Note that these
questions make *no* assumption about the role of the network's
function in such nebulous phenomena as consciousness.

My working hypothesis is that the brain of most fetuses is an
adequate substrate out of which one could construct a network.  
The network need not be identical to the adult version in order
to be capable of mental function.

[Pant, pant] This is the very best of my understanding of the
complex networking of the brain, and it must be said that network
theories of "how the brain works" are a dime a dozen.

[deletia]

>>> A weak analogy on my part, admitedly. However, in the case you cite,
>>> that of chronically demylinated fibers, it should be pointed out that
>>> the function regained is sporadic and subject to severe limitations.
>>> I've said before this is out of my field, but my recollection is that
>>> such regained function is limited to gross motor control. I don't
>>> think thought processes would be possible with such limited neural
>>> activity (strictly an opinion, obviously) no matter how "gross" our
>>> thoughts may be, at times. :)

>>Well, large segments of the nervous system function quite nicely
>>in the absence of myelin, suggesting that the failure rate is
>>not a big issue.  Your point that "thought processes" might require
>>higher standards for fidelity than, say, the sympathetic nervous
>>system is well-taken but little more than an assumption.  The
>>possibility that fetal mentation is present, but quantitatively
>>different from that of adult humans, remains and is, IMO, not
>>insignificant.

> Which large segments function "quite nicely" without myelin?

The olfactory system is a good example.  The olfactory nerve
contains millions of fibers innervating the olfactory bulb, and
not a one is myelinated.  Consider also the molecular layer of
the cerebellum.  It contains the millions of parallel fibers,
axons of granule cells.  Unmyelinated.  Pick up a copy of
_The Fine Structure of the Nervous System_ by Peters, Palay and
Webster and flip through some electron micrographs of peripheral
nerves or CNS white matter.  You'll see, in peripheral nerve,
huge myelinated fibers at times swimming in a sea of little
unmyelinated fibers.  In the peripheral nerve, these may be
postganglionic sympathetic axons, or unmyelinated sensory axons.
Pain fibers, for example, are thought to be largely unmyelinated
I believe.  In any case, it is clear that the nervous system
transacts a significant amount of its business without the help
of myelin.

> The only demyelinating disease process I've had experience with is
> Guillain-Barre' syndrome (acute ideopathic polyneuritis).
...........[deleted discussion of G-B].................
> Further, we know that in early pregnancy, these same
> roots must be myelinated before movement (other then twitches, which
> occur as much from random excitability of the muscle tissue as
> anything) takes  place i nthe fetus. Considering this, and considering
> how much more complex the electrical activity of thought must be, do
> you not think it is resonable to say that thought is unlikely to be
> present?

Again, I feel the utility of using *demyelination* of previously
myelinated fibers as a study of the general importance of myelin
is extremely limited.

[Large deletion]

>>> I tend to take the opposite (and less absolute view) that if you can't
>>> prove it exists, then it is safe to assume that it does not. While
>>> there are plenty of examples of cases where this turned out to be
>>> false, it can be defended as making judgements based on the best
>>> available information. 

>>Can you prove that consciousness exists?

> To my own satisfaction, yes. But if "personhood" is based almost
> wholey on subjective data and personal philosophy, isn't
> "conciousness" as well?
> If we define conciousness as the ability to respond intentionally to
> oputside stimulation, then I think we can show it's existance. The
> "intentionally" qualifier rules out the reflex motions o a fetus is
> capable of, but also puts neonates on shakey ground.

Behaviorists would conclude that consciousness does not exist.

>>On a different tack, if I show that the developing brain of a
>>6-week-old fetus is busily firing impulses (long before "brainwaves"
>>can be detected by an EEG), then I can make a case for the
>>POSSIBILITY of mental function.  Of course, I can't prove it
>>exists, but this makes the situation quite different than, say,
>>the contention that Elvis is alive on Mars.

> Of course he's not, or I couldn't speak for his ghost. ;-)
> The mass of tissue in a 6 week embryo (not fetus, not until week 9, as
> you pointed out to another poster... )

Whooooopsie daisy.

> which may eventually become a
> brain may well be firing impulses. But does it qualify as "mental
> function" (which I take to mean some relation (cousin, perhaps) to
> intelligence)? Motor neurons fire at random, even in adults (you've
> seen peopel twitch), so it can be assumed (or proven, possibly) that
> others do as well. But for it to qualify as some omen of developing
> intelligence, it would need to be (to me anyway) organized. 
> I don't put much faith in the EEG, honestly. I've a friend in the
> neurophysiology area who has been known to say "I can get an EEG of 3
> cells in a petri dish." It's a far cry from the brainwaves seen in
> adults, or even neonates, but it is an EEG...

Nah.  It's an electrophysiological recording of a membrane potential.
The prefix -encephalo- would seem to exclude cultured neurons.

A detectable EEG signal is proof of electrophysiological brain activity.  
Lack of a detectable EEG signal is proof that whatever activity is
present cannot be detected by an EEG.  Doesn't take that much "faith"
to deal with that.  It does take a healthy understanding of what an
EEG is (and isn't) to extract meaningful information from the trace.

[Deletia.  More deletia.]

>>I am resigned to the reality of choice being left to women and
>>abortion providers.  That's why I think it's worthwhile to 
>>discuss the moral issue of abortion (in this case by discussing
>>scientific aspects of the personhood question).  While I agree
>>that the fetus mustn't outweigh the mother, I reject the notion
>>that the conflict is between "potential" and "reality" and assert
>>instead that it is between 2 different realities.

[Small deletion]

> I can agree with you on the different realities idea.
> We both see pre-birth "personhood" as a possiblity. I think the main
> point of difference we have is that you choose to make any error (wrt
> this possibility) in favor of the fetus (subject to the balancing you
> mention above), while I prefer to make that possible error on the side
> of the woman carrying the fetus.

That's a fair characterization of my position.  I would emphasize
your use of the word "choose" and reiterate that my arguments, at
present, make no claim regarding the appropriate use of legislation.
I, of course, would love to see more people make the same choice.

[Highly technical references to scientific alliteration deleted]

>>> BTW Steve, you forgot to include a gratuitous insult... Are you
>>> slipping up? ;)

>>Slipping up?  No.  Cracking up?  Why yes, you pathetic pile
>>of primordial soup.  Was that gratuitous?  I'd better look it
>>up...

> HA! You admit you don't have the dictionary memorized? What sort of
> t.a poster are you? Did your last EEG get reverse polarization and fry
> that miserable excuse for a brain of yours??

Yeah, but so what?  Intelligence resides in the nipples.  You can't
prove it otherwise, so it must be true.  And you can bet I'd be
pretty nervous before an EKG...

--

Steve Matheson   Program in Neuroscience   University of Arizona
sfm@neurobio.arizona.edu