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From: rod@VENERA.ISI.EDU (Rodney Doyle Van Meter III)
Newsgroups: sci.nanotech
Subject: Re: How big is a brain?
Message-ID: <8904131959.AA02594@athos.rutgers.edu>
Date: 31 Mar 89 23:26:31 GMT
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In article <8903240502.AA22884@athos.rutgers.edu> csimmons@oracle.COM (Charles Simmons) writes:
>
>
>How hard will it be to actually simulate a neuron in silicon?  ("Very hard"
>is not a sufficient answer.)  Do we have to simulate the location and
>movement of most molecules in the neuron?  That is, is a significant
>fraction of the state information of a neuron stored in the chemical
>composition of the neuron?  Or can we get by with a piece of hardware
>that looks like an op-amp that has about 500 inputs and 500 outputs?

Carver Mead has had what he calls an analog VLSI neuron for at least
three years, if not longer. It can have a number of inputs, integrates
the current coming from them, and eventually fires off a pulse, then
has a recovery time before it can do so again. I think they also have
negative inputs worked out. Sounds like a simple neuron to me. They
need to scale up a bit in the number of inputs, and the last I heard I
think they were still at <1000 per chip, I think in the 100 range for
certain purposes. All the same, tremendous progress. Their clock
speeds are also naturally much higher than the chemically driven
neurons. Their current applications include work in the vision area,
and an imitation cochlea (both of these have >1000 elements, but I
don't think they were all neurons. All the same, my earlier numbers
may be wrong.). You'd have to ask someone else for better details.

My question: my understanding of the brain and memory is poor, even by
current standards. I think I heard, though, that short term memory is
stored in the synapses, in electro-chemical form, and long term memory
(learning) involved a gradual, directed rewiring of the brain. IF this
is correct, how do the analog VLSI guys intend to manage this?

		--Rod
		  rod@ISI.Edu