If it is now widely accepted that sleep is important for memory consolidation, we do not know the exact role of sleep in this process. The purpose of my thesis project was to dissect the relationship between sleep and memory. To do so, we have analyzed the impact of short sleep deprivations on olfactory memory consolidation in Drosophila. In flies, a conditioning session, consisting of an odor associated with electric shocks, induces associative olfactory memory. A massed conditioning generates a consolidated memory form called Anesthesia Resistant Memory (ARM), whereas a spaced conditioning, with rest intervals, induces Long-Term Memory (LTM). ARM and LTM can both last for days but, importantly, unlike ARM, LTM is an energetically costly memory that depends on de novo protein synthesis. My results show that sleep deprivations affect LTM and, more unexpectedly, also ARM. This effect can be compensated at the step of memory retrieval if flies are tested just before lights-off, a period associated to an increase in fly locomotor activity. These results highlight: i) a functional interaction between the consolidation and the memory retrieval steps, and ii) that circadian factors influence the memory sensibility to sleep loss. Lastly, we have also shown that a sleep deprivation taking place right after conditioning, not only does not impair memory, but exerts a positive effect on memory consolidation. This work points to complex correlations between circadian rhythms, sleep, and the retrieval step of consolidated memories in Drosophila
