Spontaneous turning behaviour by Dictyostelium discoideum slugs.

Dictyostelium discoideum slugs migrating in the absence of external stimuli tend to continue migrating in the original randomly 'chosen' direction. Spontaneous deviations from the starting direction accumulate with time at a rate that measures the 'physiological noise' in the slugs' steering mechanism. Most of the spontaneous turning signals arise in the transduction chain 'downstream' of the convergence of photosensory and thermosensory processing, and the site(s) of action of the mutation pho-355. A significant amount of steering 'noise' arises 'upstream' of the site(s) of action of fluoride (which has specific effects on phototaxis and thermotaxis).