C. elegans

[Ernst Miebur]

Concerning the question whether someone did simulate the nervous
system of C. elegans:

I did a simulation of the somatic motor system, which controls the
movement of all the major muscles of the worm and which comprises
about 20% of all neurons (Niebur & Erdos, Computer simulations in
networks of electrotonic neurons. In: R. Cotterill (ed.), Computer
Simulations in Brain Science. Cambridge Univ.  Press,148-163, 1988.
This is a preliminary paper which describes some of the methods used.
I have some newer papers in preparation that I will send you on
request.)

To the best of my knowledge, this is the only detailed simulation
of the nervous system of a nematode (and I am pretty sure that it is
the largest fraction of ANY nervous system ever simulated in detail).

I agree with you that nematodes are a fascinating model system. In
particular, if one takes into account that there are many species of
very different sizes but with similar structure of their nervous
sytems. This makes possible complementary experiments, like
determining the ultrastructure at the synaptic level in small species
(like C. elegans) and doing electrophysiology in large species (like
Ascaris lumbricoides). In fact, the news is even better: Not only all
the C. elegans neurons have been mapped, but also ALL the other cells!
And: This is the case in ALL stages of the development, from the
fertilized zygote to the adult. In this sense, C.elegans is certainly
the best known of all animals. If you want any further references to
this work, I will be happy to provide them.

You are wondering whether the connectionist approach can get any
justification from a simulation of C. elegans. The answer is very
clear: NO WAY! The connectionist model
("sum-unit-cum-squashing-function")
is a lousy model for this system.  I wouldn't even call it a model,
any simulation based on this model would be too far away from anything
reasonable in this system. Draw from this whatever conclusion you want
for other systems, but I think that in this system, no serious worker
would dispute Jim Bowers view that a detailed knowledge of Biology is
important. 

Ernst Niebur
ernst at descartes.cns.caltech.edu


PS The number of neurons (in the wild-type hermaphodite) is not 329
but 302.