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Article 5414 of comp.ai.philosophy:
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>From: erwin@trwacs.fp.trw.com (Harry Erwin)
Newsgroups: comp.ai.philosophy
Subject: Re: syntax and semantics
Message-ID: <571@trwacs.fp.trw.com>
Date: 5 May 92 12:15:18 GMT
References: <1992Apr8.215800.18021@mp.cs.niu.edu> <92099.194744JPE1@psuvm.psu.edu> <1992Apr9.174840.3407@organpipe.uug.arizona.edu> <5674@mtecv2.mty.itesm.mx> <2@tdatirv.UUCP>
Organization: TRW Systems Division, Fairfax VA
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sarima@tdatirv.UUCP (Stanley Friesen) writes:
...
>|We can't equate neurons
>|to microprocessors, since we don't know yet how a neuron works.

>WRONG me bucko!   We *do* know, in large part, how a neuron works.
>We may not know the smallest details, but then that is true for every
>branch of science - we do not know all there is to know about particle
>physics either.
...
Which model of neuron functioning are you refering to? The computer
science variant (highly oversimplified) or the neuroscience variant (which
frankly admits its ignorance). Dowling and Boycott pointed out in 1965
that few neurons in the eye prior to the ganglion cell layer generate
nerve impulses, and all interactions are via graded polarization.
(Dowling, J. E., and Boycott, B. B., 1965. "Neural connections of the
retina: Fine structure of the inner plexiform layer." Quantitative Biology
30:393-402.) How do you deal with non-traditional networks of neurons,
where the interaction occurs in the dendritic arbor? 

In this context: has anyone looked at the evolution of neural network
components? The neuron, although primitive, is a complex beastie. What is
a realistic evolutionary sequence from ectoderm cell to basic neuron?

Just for a laugh: Christen, Ratto, Baroin, Perasso, Grell, and Adoutte
(1991) claim to have shown that plants, diploblasts (cnidaria, ctenophora,
and porifera), and triploblasts (the remaining metazoan phyla) are derived
independently from a protist assemblage, with plants and diploblasts being
more closely related than either are to triploblasts. They come to this
conclusion from RNA sequencing data. One implication of this result is
that the neuron predates multicellular life, since it is found in both
diploblast and triploblast phyla. The reference is Christen, Ratto,
Baroin, Perasso, Grell, and Adoutte, 1991. "Origin of Metazoans: a
philogeny deduced from sequences of the 28S ribosomal RNA." in Simonetta
and Conway Morris, 1991. The early evolution of Metazoa and the
significance of problematic taxa. Cambridge University Press.

Cheers,
-- 
Harry Erwin
Internet: erwin@trwacs.fp.trw.com



