Edelman's Theory of NGS

Jim Hutchins hutchins at fiona.umsmed.edu
Thu Sep 7 18:16:53 EST 1995


Jason L. Eriksen (jerikse at news.luc.edu) wrote:
: I'd like to start off this thread by calling for the erudite scholars of

Who're you callin' erudite, bub? :-)

: this group (that means YOU!) to contribute your thoughts about Edelman's
: theory of neuronal group selection.  After having completed 
: _Neuronal Darwinism_, I was impressed with the depth and breadth of his
: knowledge, and the book served to crystallize a number of concepts that
: I had been mulling over for years, but never formally categorized.

: It would be especially gratifying to hear modifying views of Edelman's 
: grand scheme.  How valid, for instance, is the proposal that CAMS and
: SAMS are the guiding principal behind formation of primary neuronal groups,
: as opposed to a more generalized peptide related system? 
[stuff deleted]

That's the problem in a nutshell.  Why do these have to be the *only* two
possible mechanisms?  I must confess, I put down _Neural Darwinism_ about
halfway through.  I believe Dr. Edelman began to repeat himself.  And to
propose that these are the only two mechanisms, well, I find that an
example of a 'straw man' argument on Dr. Edelman's part.  He well knows that
there are many, many more competing theories of what he calls 'neuronal
group selection'.  In fact, I have never seen the term adequately defined,
so I'm not even sure what I'm getting so worked up about :-).

To paraphrase Hamlet, 'There are more things in brain development than are
dreamt of in your philosophy'.  I would propose that there are many such
basic mechanisms, and that *all* of them operate to one extent or another in
any system you care to mention.  To wit: timing of neuronal outgrowth; 
differential adhesiveness (a la Edelman and others); correlated activity;
anterograde and retrograde 'messengers' (growth factors and/or neurotrans-
mitters); classical tropic and trophic mechanisms; etc.  In fact, looking
over this short list, there's lots of overlap even between these categories.

My experience in nervous system development has been that any one mechanism 
is inadequate to explain the behavior of the developing system and any one
perturbation either causes little or no discernable effect or collapses the
whole thing.  This suggests to me (but certainly does not prove) that a lot
of different mechanisms exist, and that fiddling with one allows the others
to 'take over'.  On the other hand, smashing the developing nervous system
with a hammer stops neural development, but tells us little about the
mechanism.

Now that I'm on my soapbox, I would encourage everyone to be a little more
inclusive in their thinking about developmental mechanisms and a little
less catholic (that's with a little c on purpose) in their theories.

[specific examples of Neural Darwinism deleted]
: Is network formation a collection of modified Hebbian rules in the
: Secondary network formation, or are non-deterministic elements 
: and stochastic
: elements involved?  Is Penrose's idea of Quantum indeterminancy
: as an element of consciousness neurologically valid, or pure bushwah; 
: does Stocastic Resonance greatly change the rules of neural network 
: formation?

I have no idea what most of the words in the preceding paragraph mean.  I
become suspicious at terms like 'quantum indeterminancy' or 'stochastic
resonance'.  I know what 'Hebbian' means, I've read Hebb.  However, in my
opinion, the term 'Hebbian' has been expanded beyond what was originally
proposed.  (Which is fine, because I use the term in the 1990s sense myself,
and not in the original 1940s sense.)  To put it briefly, network formation
is a collection of all the rules you can think of, and a couple more neither
one of us has thought of yet.

'These are the only ones of which the news has come to Harvard/There's
many, many others but they haven't been disc-cah-vered'--Tom Lehrer.
--
Jim Hutchins
Assoc Prof Anatomy, Asst Prof Neurology (Research), Univ Mississippi Med Ctr
http://fiona.umsmed.edu/~hutchins/    ***    E-mail:   hutchins at umsmed.edu
``It became necessary to destroy the town in order to save it.''--American
infantry officer firing on Ben Tre, Vietnam, 2/8/68



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