Figure 1.

Radula movements in freely behaving Aplysia. In the absence of food (A) or under continuous inciting stimulation with non-ingested food applied to the lips [Stim., (B)], Aplysia spontaneously generates repeated cycles of protraction and retraction of its tongue-like radula (vertical bars). The distribution in time and the duration of radula movement cycles are highly variable and are not determined by any explicit sensory cue, although the mean frequency of cycle occurrences increases during inciting stimulation. Between successive radula cycles the animal engages in various other actions including lip movements, head-waving or locomotion which are all directed toward effective food seeking.