[From Bill Powers (2008.07.06.1945 MDT)]
Interesting study in Nature of C. Elegans, a flatworm, I think, and one
of a number of creatures that steer by the random-walk chemotaxis method
of e. coli.
Suzuki, H., Thiele, T.R., Faumont, S., Lockery, S.R., & Shafer, W.
R.; Functional Assymetry in Caenorhabditis elegans taste neuronxs and its
computational role in chemotaxis. Nature 454, 114-117 (3 July
2008).
By applying step-changes in the concentration of NaCl to the animal, the
authors shows that there are neurons that respond to the rate of change
of concentration; one kind of neuron (ASEL) responds to positive rates of
change, and another (ASER) responds to negative rates of change. By
various means the authors established that these responses made
“significant contributions” to “run” and
“turn” behavior. Almost 30 years ago, Koshland showed that E.
coli could sense rates of change of concentration of 27 substances, and
that these changes contributed to delaying or advancing the time at which
tumbles took place – and provided me with the model I needed for
reorganization.
E. coli has no nervous system; it’s interesting to see the same principle
showing up in more advanced organisms.
Best,
Bill P.