From: sfm@manduca.neurobio.arizona.edu (Stephen Matheson)
Newsgroups: talk.abortion
Subject: Re: Spoken Like a True ProLifer
Date: 11 Jan 93 06:56:35 GMT
Organization: University of Arizona UNIX Users Group

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):
>>> In article <1993Jan8.193440.26552@organpipe.uug.arizona.edu>
>>> sfm@manduca.neurobio.arizona.edu (Stephen Matheson) writes:
>>>>From article <1993Jan6.200941.13165@mnemosyne.cs.du.edu>,
>>>>by mcochran@nyx.cs.du.edu (Mark A. Cochran):
>>>>> In article <1993Jan6.183814.1552@organpipe.uug.arizona.edu>
>>>>> sfm@manduca.neurobio.arizona.edu (Stephen Matheson) writes:
>>>>>>From article <1993Jan6.162256.4767@mnemosyne.cs.du.edu>,
>>>>>>by mcochran@nyx.cs.du.edu (Mark A. Cochran):
>>>>>>>>=vengeanc


[Sigh. Deletia.]

>>> 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.

>>> (exam record of patients who have
>>> been demylinated for supporting evidence)

>>Here I can say with confidence: a demyelinated fiber is not the same
>>as a premyelinated fiber.  A demyelinated fiber cannot conduct because
>>the myelination led to the concentration of sodium channels at the
>>nodes.  Removal of the myelin leaves the fiber with widely-separated
>>islands of excitable membrane, with no way to regenerate the impulse
>>in between.  I believe that some function is regained in chronically
>>demyelinated fibers, due to the gradual spreading of the ion channels
>>throughout the membrane.  At this point, it becomes similar to a
>>premyelinated fiber: capable of conduction, but at a slower velocity
>>than in the myelinated condition.

> 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.

>>> we can theorise that
>>> mylination is at least *one* stage of development that needs to be
>>> reached before thought can take place.

>>Theorize to your heart's content; I love to discuss theories.  If
>>you want to see me go ballistic, write up your theory as though
>>it's a fact, then publish it in the non-peer-reviewed journal
>>_Parade_ magazine.  You'd at least get applause from a misguided
>>planetary scientist.

> I don't even *read* _Parade_ so we don't have to worry about this...

You don't need to.  It's been cited at least once on t.a in support
of the must-have-cortex-and-synapses-and-brainwaves-to-think-and-
therefore-to-be-a-person theory of personhood.

[Large deletion]

>>>>> The reson I insist on proof of
>>>>> presense, not the absense, is simple. Lack of proof in favor of
>>>>> existance can be considered to resonably show nonexistance.

>>>>True, it *can* be considered as such.  But should it?  Jeffrey James
>>>>Price just got a taste of the consequences of a similar (but admittedly
>>>>not equivalent) assertion.  (Check it out.  I predicted that he would
>>>>see a truckload of examples of the consequences of his idiotic
>>>>reasoning.  My favorite: "There are exactly 223 chemical elements.")

>>> I missed this, sounds like it was a real fun flamewar. :)

>>Pretty one-sided, actually.  His contention (paraphrased with
>>amazing accuracy): you can't prove it (z/e/f personhood) false,
>>therefore it's true.  Fun it was.

> 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?

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.

[More stuff about Mr. Price deleted.  Poor guy.]

>>My point was that
>>looking for something and failing to find it is *NOT* tantamount
>>to disproving its existence.  People looked at nervous tissue
>>through microscopes for generations, and couldn't see synapses.
>>Some concluded that they didn't exist, and their "reticular
>>theory" of the structure of the nervous system survived till the
>>50's, when Palay and Palade took the first electron micrographs
>>of synapses.  I think there's a lesson there.

> I think I understand your point. The problem I see is that we aren't
> *just* discussing theory. If we were, there would be no controversy. I
> am not about to claim that the information we have is 100% accurate.
> I'm not that fond of being flamed. :)

Your caution is well-advised, and, in my experience, somewhat rare.

> But we do have to make decisions. Despite the uncertainty of our
> theoretical knowledge, there are real women with real pregnancies
> trying to figure out what to do about them. I'll admit that we are
> destroying a fetus of unknown potential. (It's just as likely to grow
> up to be a serial axe murderer as it is to find a cure for the common
> cold, though.)

It's more than likely going to grow up to be a rather average
individual whose value is, IMO, equal to the 2 examples above.

> So what do we do?
> I don't think there is going to be a good answer, not for everybody.
> That's my main reason for advocating leaving the choice to the
> pregnant woman. I don't think the potential of the fetus can outweigh
> the reality of the woman.

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.

> On another note... Have you ever noticed the tendancy of researchers
> and authors of medical texts to work with others with similar names?
> Examples: Palay and Palade, Waley and Wong, Potter and Perry, Hill and
> Howlett...

You left out Hodgkin and Huxley just to irk me, didn't you?! :-)
Well, you said you're not into neuro, so...

> 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...


--

Steve Matheson   Program in Neuroscience   University of Arizona
sfm@neurobio.arizona.edu
Newsgroups: talk.abortion