From: mcochran@nyx.cs.du.edu (Mark A. Cochran)
Subject: Re: Spoken Like a True ProLifer
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Date: Wed, 13 Jan 93 02:36:36 GMT

In article <1993Jan12.182214.7036@organpipe.uug.arizona.edu> sfm@manduca.neurobio.arizona.edu (Stephen Matheson) writes:
>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? :-)
>
Yes, since that is the essence of t.a :)
I'm under the impression tha tthere is more then one kind of
redundancy.In this context, we could have path redundancy, in which a
single impulse would be transmitted over a branching series of
alternate pathways. Or signale redundancy, in which a single stimuli
results in multiple impulses from multiple focal points.

>> 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.
Certainly a valid theory. But how does it account for the observed
loss of mental accuity/ability/agility when the brain (network) is
damaged by disease/trauma/whatever? Is it your hypothesis that the
network will function when it is above a certain size (number of
interconnecting neurons) or when it is at or above a certain
percentage of the available neural connections (i.e. a smaller number
of connections is needed by a physically smaller brain), or something
altogether different?

>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.
>
Again, we have reached a point in which there is no longer a way to
prove an answer scientifically. Unless we can figure out a way to grow
a brain without myelination (since you have already pointed out the
difference between demyelinated and never myelinated neurons) we will
never havea way to compare and observe.

>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.
>
If one could construct such a network, does thta not iimply that it
does not already exist? There's no denying that the potential for the
network (and the resulting thought) is there.

>[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.
>
Last time I checked, they'd gone down to $0.07 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
Sorry, I thought you said large, I kind of thought the olfactory
system was relatively small. ;)
I'm also guilty of getting confused by the length of our posts. I'm
still thinking in terms of demyelinated, not never myelinated. Comes
from our different viewpoints, I suspect.

>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
There's that alitteration again... Is this a conspiracy?

>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.
>
That's one theory, yes, but I think it's got some pretty stiff
competition. The gate theory of pain conduction (as I recall) relies
on myelinated fibers.

>> 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.
>
How about the lack of activity in pre-myelinated neurons I mentioned?
Is there a structural/chemical/whatever difference between a
pre-myelinated fiber and a never myelinated fiber?

>[Large deletion]
>
>>>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.
>
I'm not a behaviorist. :) Are you?

>>>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.
>
*chuckle* I couldn't resist. ;) At least I'm not asking you to clarify
if you're talking LMP or gestational age. I'm assuming that we're both
talking gestational age, since it's a bit more accurate.

>> 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.
>
How about artificially stimulated human 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.
>
By this definition (not sensitive enough, rather then no activity) we
need a new way to define legal death then. Otherwise, we have to
assume we're burying people who are not dead, but merely not producing
enough signal to pick up.

>[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.
>
Your lack of legislative ardor is one of the reasons why it is
possible to carry on a debate with you. From my point of view, if the
pro-life side has a valid argument, it should be able to stand on it's
own merits, without the need for legislative force.
That is, to me, one of the reasons for being pro-choice. Lacking a
definative answer, I'm unwilling to limit options for pregnant women.
Despite what some in this forum will say, this does not make me
pro-abortion. I would just rather we treated the problem (unwanted
pregnacies) instead of the symptom (abortion).

>[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...
>
You know, I can think of a couple people who probably *do* think with
their nipples. I'll have to ask the Ghost of Elvis (when he returns
from mars) to make sure.

--
                  Mark Cochran          merlin@eddie.ee.vt.edu
These are the views of my employer, your employer, your government, the
Church of your choice, and the Ghost of Elvis. So there.
Member, T.S.A.K.C.
Newsgroups: talk.abortion