  Cells can show not only spontaneous movement but also tactic responses to
environmental signals. Since the former can be regarded as the basis to realize
the latter, playing essential roles in various cellular functions, it is
important to investigate spontaneous movement quantitatively at different
physiological conditions in relation to cellular physiological functions. For
that purpose, we observed a series of spontaneous movements by Dictyostelium
cells at different developmental periods by using a single cell tracking
system. Using statistical analysis of these traced data, we found that cells
showed complex dynamics with anomalous diffusion and that their velocity
distribution had power-law tails in all conditions. Furthermore, as development
proceeded, average velocity and persistency of the movement increased and as
too did the exponential behavior in the velocity distribution. Based on these
results, we succeeded in applying a generalized Langevin model to the
experimental data. With this model, we discuss the relation of spontaneous cell
movement to cellular physiological function and its relevance to behavioral
strategies for cell survival.
