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worms which provides a qualitative comparison of their model and actual worm
pathways (see Ferrée & Lockery, 1999, p. 270).
Next, Ferrée and Lockery explored the linearized equation solution to develop
a more intuitive result, since they note that 'distributed representations' often
lack this property of intuitability. This part of their paper provides a 'simple
rule for chemotaxis control which relates the body rate of turning … to time
derivatives of the chemosensory input ' (p. 23). On the basis of the analysis,
Ferrée and Lockery argue that their network uses strategies both of klinotaxis
(alignment with a vector component of the stimulus field) and klinokinesis
(change in turning rate in response to the scalar value of a stimulus field)
to produce the behavior represented in their Fig. 3b. (Here the definitions of
klinotaxis and klinokinesis follow Dunn, 1990.) These strategies also suggest
seeking additional experimental worm stimulus and movement data to confirm
or disprove the models.
Ferrée and Lockery's approach does not use genes, and it does not employ
structural data from molecular biology. It does utilize physiology and neuro-
scientific compartment analysis to formulate a mathematical model of a neural
network that qualitatively agrees with the worm's observed behavior. It is per-
haps more similar to a biophysics approach such as H and H's action potential
model than a biomolecular approach.
5.
IMPLICATIONS OF THE FERRÉE AND LOCKERY MODEL
FOR
C. ELEGANS
CHEMOTAXIS
The F and L model is a mathematical simulation of
C. elegans
chemotaxis
relying on a simplified neural circuit, and on generally accepted model-building
strategies found in the neurosciences. Like H and H, it seeks to identify an
appropriate level of abstraction from the much more complicated details that
might constitute the specific mechanisms of neural interplay. But thus far it
has not enjoyed the broad acceptance and heuristic fertility of the H and H
model. Why that is the case needs further thought, since the general strategies
appear to be similar. Possibly, what seems to be the idiosyncratic aspects of
the model arise because F and L are not dealing with a constituent low-level
mechanism that could be found in multiple instances and more easily generalized
to similar ion channel activities in related type of cells. Rather F and L deal with
an intentionally particular wiring diagram that may restrict the generalizability
of the results of their model. However, the more methodological modeling
and equation building and solving strategies may have broader applicability,
such as the reliance on an empirically confirmed circuit, and the application of
compartment modeling to such interactive networks.
