X-Message-Number: 25956
Date: Fri, 1 Apr 2005 09:17:30 -0500
From: Thomas Donaldson <>
Subject: reply to Yvan Bozzonetti

To Yvan Bozzonetti:

Sorry, but you haven't dealt with my comment at all. The most crucial 
point about our dentate gyrus, which is a part of our hippocampus, is
that it CREATES AND USES NEW NEURONS. You haven't answered that part of
my comment at all.

As for using a faster brain with fewer processors, that creates a 
problem, too. We're talking about a parallel system in which many
different processors all do different things. In normal computing
terminology a processor does one thing at any instant of time. Sure,
if its fast enough we slower humans may think that it's doing 
these things simultaneously, but that's not what's happening. And
when you have different processors (neurons) each doing something
different, there's no way to collapse them into only one processor.
Even when different processors only sometimes do different things,
the same problem occurs.

This is of course why computer people are so interested in parallel
processing. If you want to solve a single VERY LARGE matrix problem,
the best way to do so is to break the problem up into pieces and
have different processors do each piece, and then make the step
of combining them as parallel as you can. No matter how fast your
individual processors may be, you can make a computer even faster
by having them work as much as possible in parallel. When we consider
the millions of neurons in your upper brain, it ceases to be at
all obvious that we can imitate them with faster but fewer processors.
There are just too many --- perhaps someday, but not soon.

But the most critical point remains growth and change, which you
did not discuss at all. Neurons appear and disappear, and so do
their connections (synapses). 

And as a postscript, I'll add that I'm not saying that neurons 
can't be improved, or that some system with the same characteristics
might be built of quite different materials than biological brains.
I am saying that unless you can produce a system with as much
growth and change as a brain, your belief that you can build a
brain is a delusion only.

          Best wishes and long long life for all,

               Thomas Donaldson

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