From: sfm@manduca.neurobio.arizona.edu (Stephen Matheson)
Newsgroups: talk.abortion
Subject: Re: Brain Function in Anencephalic Infants
Date: 15 Dec 92 03:44:18 GMT
Organization: University of Arizona UNIX Users Group

From article <Bz7xp7.MLH@news.cso.uiuc.edu>, by parker@ehsn21.cen.uiuc.edu
(Robert S. Parker):

> dsholtsi@csl36h.csl.ncsu.edu (Doug Holtsinger) writes:

>>In article <Byv2I4.5y7@news.cso.uiuc.edu> 
>>parker@ehsn21.cen.uiuc.edu (Robert S. Parker) writes:
>>>dsholtsi@csl36h.csl.ncsu.edu (Doug Holtsinger) writes:

[extensive deletia]

>>Various claims were made that myelination of the brain was necessary 
>>in order for sentience or "thought" to appear, but these claims have  
>>never been proven.  The fact that some medical textbook claims that
>>myelination begins at 24 weeks does not prove that myelination is
>>necessary for sentience or "thought".  In fact, I posted evidence 
>>showing that myelination was NOT necessary in order for neurological 
>>function to appear:

> "thought" is not the same as "neurological function".  All mature
> animals have "neurological function".

>>   Brain Maturation and Cognitive Development
>>   Edited by Kathleen R. Gibson and Anne C. Petersen
>>   Aldine De Gruyter Publishing, 1991
>>   pg. 30

>>  "As axons can propagate impulses prior to myelination, myelination is
>>   not an indicator of functional onset (Ulett et al., 1944, 1950).
>>   Rather, myelination is a late developmental event and an indicator
>>   of functional efficiency and specificity. Myelination data, then,
> [      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^    ]
>>   may be considered estimators of those aspects of neural maturation
>>   and function related to speed and specificity of nerve transmission."

> In other words, prior to myelination, the creature has the mental
> capacity of a slug.

The quoted passage neither says nor implies this.  It would be fascinating
to see if anyone anywhere has any *scientific* reason to believe your
assertion.

>>   pg. 188

>>   In both rats and humans, neurological function begins before myelin
>>   appears.  In many species[,] critical functions in the adult, such as
>>   those of the autonomic nervous system, occur in normally unmyelinated
>>   [nerve] fibers.  Many invertebrate nervous systems function without
>>   myelin, and anatomically specific demyelination does not invariably
>>   result in the expected loss of function in clinical syndromes such
>>   as multiple sclerosis." 

> I don't see any reference to "thought" in this quote; it is talking about
> autonomic functions and motor-control (which are present in all mature higher
> animals, not specific to "people" or even to "humans")

The original point is well-taken.  The point that myelin is not
necessary for neurological function is relevant in any debate about
its role in ill-defined mental phenomena.  If not impulse propagation
or even regional function (e.g. in the autonomic nervous system), what
is it about myelin that makes it so critical for "thought"?  Those
who advance these tenets of faith seem unable to provide scientific
evidence for their musings.

>>> [... Carl Sagan article ...]

[Neat stuff about sentience deleted]

>>              Carl Sagan's article suggests that the capability for
>>"thought" and "reason" doesn't occur until after the 6th month of 
>>pregnancy.  I posted evidence showing that it appears sometime
>>after birth:

> You still don't get it.  The 6th month is the *earliest* that it could
> *possibly* occur.  That does *NOT* exclude the possiblity that it doesn't
> actually occur until after birth.  (which I mostly believe)  Your evidence
> does not contradict Sagan at all.

It's true that the evidence presented doesn't contradict Sagan.  In
order to contradict Sagan, one would need evidence that thinking occurs
in certain anatomical structures (microscopic or macroscopic) in
the brain.  If one were to claim possession of such evidence, one
would be guilty of Sagan's unfathomable and wholly disgusting
irresponsibility.  I've received some really interesting email
from a colleague who expressed the same disgust for Sagan's drivel,
and he pointed out that Sagan has championed long-rejected theories
of neurobiology before (i.e. the tripartite theory, in Dragons of
Eden; I've not read it).

> (In fact he probably knew about it himself
> if it was published before the article that was quoted.)

I doubt it.  But I don't think it would have mattered; Sagan was
articulating assumptions and articles of faith, not science.

>>  "Advanced sensorimotor intelligence, as defined by Piaget, emerges
>>   at the same time the neocortical association areas begin to 
>>   myelinate.  

>>   ... [F]rom the age of 1 to 2 years in the human, all cortical areas
>>   and most cortical layers are myelinated to some degree.  According
>>   to PET scan data, all cortical areas in the human neocortex also
>>   exhibit high degrees of glucose utilization by 1 year.  Thus, all
>>   cortical areas are probably functional between 1 and 2 years of
>>   life in the human...  Cortical maturation from that point on 
>>   involves increasing efficiency or complexity of function of areas
>>   that are already functioning at least in rudimentary form by late
>>   infancy.  All cortical areas continue to gain myelin subsequent
>>   to late infancy, but the most dramatic changes in myelination
>>   occur in the cortical association areas.  The upper layers of
>>   the cortical association areas do not begin to myelinate until
>>   4 to 8 years of age and emerge as prime candidates for the
>>   mediation of maturing intelligence in childhood."

>>   pg. 199

>>  "As noted by Bronson (1982), it is reasonable to think of the neonate
>>   as functionally subcortical.  Although some potential exists for
>>   function in cortical systems, behavioral and physiological data
>>   suggest that this function is extremely rudimentary."

The above passages indicate that myelination and the appearance of
certain cognitive functions is somewhat coincident.  This is the
only evidence I've ever seen cited on t.a for the various mind/body
arguments, although it is merely correlative and doesn't specifically
support the unprovable "thinking" assertions.  Note that the phenomena
are specific and measurable (at least in a sense) and that the statements
are appropriately qualified (e.g. "These areas are considered to mediate
the highest cognitive functions").

Carl Sagan's writings quoted in this thread are completely irresponsible.
His overstatement could have been accurately portrayed as unproven by
the addition of the simple phrase "in my opinion".  Only then would it
have been worthy of the great Parade Magazine.

[Rest deleted, but good stuff]

--

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