C. elegans

[Orjan Ekeberg]

Based on my experience with fairly realistic simulations of the
neuronal network producing swimming in the Lamprey (a fish-like lower
vertebrate), I would expect that much more information than the wiring
pattern is needed to produce a "working" computer model of this
nematode.  Let me give some examples.

Rythmic activity (you mention swimming) in simple invertebrates often
depends on single spikes in each cycle.  This indicates that a cell
model can not rely on an output representing only firing frequency.
There might, however, be parts of the system where a
squashing-function neuron model is sufficient.

Individual cell properties like membrane time constants, localization
of synapses, intrinsic pacemaker properties etc. probably plays a
crucial role in such a network.  Even if such properties are in
principle measurable, it is necessary to know what you are looking for
beforehand, i.e. you need a theory of the function of each neuron.  I
believe that computer simulation is an important tool when
constructing such theories.

Thus, I do not believe that it is possible to follow the strategy of
FIRST measuring everything and THEN simulate the final model.  Rather,
understanding of how a real network operates could gradually be gained
in a process involving simulations as one tool.

I do agree that, from a computational point of view, simulating 329
interconnected neurons is feasible.  We have been simulating about 600
neurons from the Lamprey including a four compartment representation
of the dendrites and Na, K, Ca and Ca dependent K channels,
transmitter and voltage dependent (NMDA) synapses, etc.  Even if the
C. elegans system might need further properties added, I think it would
still be possible to do simulations even on this level of detail.

Orjan Ekeberg

+---------------------------------+-----------------------+
+ Orjan Ekeberg			  + O---O---O		  +
+ Department of Computing Science +  \ /|\ /| Studies of  +
+ Royal Institute of Technology	  +   O-O-O-O  Artificial +
+ S-100 44 Stockholm, Sweden	  +   |/ \ /|   Neural	  +
+---------------------------------+   O---O-O    Systems  +
+ EMail: orjan at bion.kth.se	  + SANS-project	  +
+---------------------------------+-----------------------+