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machine brains

Ray Scanlon rscanlon at wsg.net
Wed Feb 17 11:43:59 EST 1999



Michael Edelman wrote in message <36C9BFFF.50AF3A56 at mich.com>...
>
>
>Ray Scanlon wrote:
>
>> What do we wish to simulate and at what level? Are we talking, for
instance,
>> of the brain of rat? This is a mammalian brain, it has all the parts of a
>> man's brain, just not so many neurons? What is the unit of our
simulation?
>> The neuron?
>>
>> The neuron is a large assortment of neurons, I have no idea how many. I
>> would be happy if someone would give me a guess or a citation as to how
many
>> in an average neuron. Some would say that until we know the story of
every
>> molecule we cannot simulate a neuron. This is hogwash.
>
>We can simulate a neuron, but we need to know more about how neurons
>interconnect. At one time we thought all neronal connections were
>axon-to-dendrite. Then we found axon-axonal, electrical, even
dendrite-dendrite
>connections. Without an understanding of all those mechanisms we can't
>completely model a single neuron.

Yes! And you can add ephaptic and hormonal effects. I say we must work with
what we have. If you insist on the life history of every molecule you are a
latter day Luddite.

>Moving up to small networks, it's only recently that the role of nitrous
oxide
>has been revelealed as a diffuse, local neurotransmitter; unless you model
that
>as well, you don't have a full model of the physical level of the brain.
And
>there's no doubt more to be discovered.


These are all just excuses for a return to contemplation of our beautiful
thoughts, our marvelous soul (mind).

>> What we simulate is what interests us. We are interested in the neuron as
an
>> electromechanical device that influences other neurons. The myriad of
>> molecular activities that have to do with the maintenance of a living
cell
>> are not involved.
>
>Ah, but they are. Axonal transport regulates the rate at which an axon can
>produce vesicles of transmitter. Availability of calcium can regulate
firing
>activity. All these can be influenced by metabolism, mitochondrial activity
and
>so on. The cell wall is pivotal in transmission of an AP to an axon. We
need at
>least a functional understanding of the relationships.


If you are serious about understanding the brain, these molecular
relationships are subsumed in the neuron as leaky integrator.

>There's a danger here in defining the question down to the point where it's
>simple, but uninteresting. Supposing you assemble 200 million of your
synthetic
>neurons into a mass and start generating S-R pairs. Do you have a mind, or
just
>an interesting programable array?


You misunderstand me. First we are to understand how the brain works, then
we are to speak of designing a thinking machine (if we wish). Note that we
talk only of design, no one should be so foolish as to think of actually
implementing such a machine.

>> The endless molecular activity of a synapse can be lumped
>> together with a few parameters. The synapse is strengthened or it is
>> weakened. The synapse disappears. there is axonal growth and new synapses
>> appear. All these are subject to a time dependence (from birth to death
of
>> the organism). A synaptic event involves a local change in the potential
>> difference between the interior and the exterior.
>>
>> This is not very much as simulation goes.
>
>It's an incomplete picture. There's a lot more going on than simple
>axonal/dedritic transmission.


Lord, yes! But not so much as to justify a throwing up of hands and a
retreat to religion.

>> There is no problem as long as we keep the soul (mind) out of it.
>
>Hmm. I think I'd argue this point. What are we trying, in the end, to
explain?
>Mind. If our brain model doesn't actually make a stab at explaining mind,
what
>good is it? It's just another hypothetical model of nothing in particular,
like
>so many other AI models.


Artificial Intelligence has nothing to do with the brain. AI is concerned
with the mechanization of the manipulative algebra of the sentential
calculus.

Explanations of the soul (mind) belong to religion. I say that theology
should be put to one side until the brain is explained. When this is done
one may turn to religion and talk about the soul (mind).

>> The brain
>> is simple and its activities are simple. We are overwhelmed by the number
of
>> neurons, by the number of nuclei, by the number of tracts, but if we lump
>> the trees together we shall see the forest.
>
>Of course, I think the forest is Mind.


Good enough! But save it until we get the brain explained.

Ray
Those interested in how the brain works might look at
www.wsg.net/~rscanlon/brain.html






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