Non-parasitic freshwater flatworms, planarians such as G. tigrina, serve as a model organism mainly due to their extraordinary regenerative capacity; moreover, their simple but centralized nervous system together with limited behavioral responses enable an almost isolated study of learning and memory in contrast to the black box of human cognition. In a large number of studies associative learning such as classical conditioning and operant conditioning has already been observed in planarians. In more recent times it has also been shown that planarians sleep, in the sense of a circadian organized quiescence, which raises the question of the connection between sleep and learning in planarians, a relationship which is well known in humans and even other invertebrates but has been overlooked by most studies on associative learning in planarians in the past. In an initial study we manipulated the day-night-rhythm, measured quiescence and the impact of subjective daytime on short term memory and a 24h long term memory within a newly established operant conditioning paradigm, the water droplet paradigm. In a follow-up study we replicated the basic procedure of the first study, additionally considering different common nocturnal simulation techniques. These consisted of redlight, infrared light and absence of light, which have been shown to elicit different behavioral responses in planarians. This allowed us to investigate possible differences in sleep-induced quiescence and learning ability. The results show that manipulation of the activity-cycle of the planarians is possible, and that the circadian rhythm is an important factor in planarian learning.