From: Damien Broderick (d.broderick@english.unimelb.edu.au)
Date: Sat Feb 12 2000 - 19:36:02 MST
At 04:21 AM 10/02/00 -0800, Robert Bradbury wrote:
>> stochastic [neural wanderings] will make the twins differ quite
>> quickly, well before birth.
>While I wouldn't disagree (given that "twins" are developing in a nutrient
>competitive situation), if you run across some scientific data I would
>like to see it. It would take some careful thought and playing with
>the numbers to determine how much actual information there is in
>genome variations and in stochastic developmental processes.
I was going on stuff at least 15 years old, but I think it's been
corroborated since. Here's a bit from my THEORY AND ITS DISCONTENTS. While
J-P C is talking abt mature brains, I read it back to an account of the
formation of the internal nets (and BTW I love his use of `singularities'...):
============
The collective-computational program [blah blah] The human equivalent has
been described by a prominent French neurologist, who borrows the somewhat
misleading medieval term `homunculus' to denote a cortical `body map' of
some discrete part of the somatosensory system:
"[I]n a given sensory homunculus, two neurons that respond in the same way
to the same sensory signal still differ in that they are not in exactly the
same position on the map and therefore are related to topographically
distinct sensory cells on the surface of the body or in the retina. If one
considers that there are about fifteen million neurons per square
centimeter of cortical surface and that in man a single homunculus can have
an area of several square centimeters, the set of singularities ... becomes
enormous. [...A]s exploration continues it becomes clear that every neuron
has its own singularity.% In reality, there is very little redundancy."
(Changeux, 1985, p. 122)#
Jean-Pierre Changeux is an unrepentant determinist, though the picture he
presents is too awesomely complex to be considered simple-mindedly
reductionist. But he insists, `The data obtained so far, although
fragmentary, are sufficient for us to safely conclude that all behavior,
all sensation, is explicable by an internal mobilization of a topologically
defined set of nerve cells, a specific graph. The "geography" of this
network defines the specificity of the function' (Changeux, p. 124).
Nobel-winning immunologist Gerald Edelman (1992) has developed a similar
selectionist account, which he dubs `neural Darwinism'. Neurophysiologist
William Calvin (1996a, 1996b) has proposed an impressive account linking
consciousness with hexagonal structures of the brain's own neural net,
which he regards as a `Darwin machine'.
%Defined p. 65: `the set of connections' `of each cell taken individually'
each of which includes the effects of `several tens of thousands of
synaptic contacts'.
# Changeux, Jean-Pierre (1985) Neuronal Man: The Biology of Mind, [1983]
trans. Dr. Laurence Garey, New York: Pantheon Books
===================
Damien
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