Sleep is a fascinating mystery that has bemused thinkers since the dawn of civilisations. Scientifically, the formalisation of sleep as an observable behaviour has been a conceptual milestone, which has enabled researchers to address the question of its ubiquity and ultimately led to the discovery of sleep-like states in most animal phyla. The fruit fly Drosophila melanogaster has long been at the vanguard of the discovery of many biological processes. In particular, it has been instrumental to explain the genetic determinism of behaviours. In the 2000s two seminal studies reported their discovery of a state of quiescence in Drosophila that had all characteristics of sleep. Rapidly, the fruit fly became a significant and widely adopted model of sleep. However, despite the large palette of advanced tools to study various aspects of the genetics, development and neurobiology, the methods and conceptual tools to investigate the behavioural aspect of sleep in Drosophila lag behind, which has limited our understanding of its phenomenology and function.

In the thesis herein, I first present the ethoscope platform, a tool to score behaviour in a large number of isolated animals. I explain how its modular design allows for large-scale, real-time, long-lasting experiments. Secondly, I provide rethomics, a general framework to analyse the large amount of resulting behavioural data, which has the potential to bridge the gap between experimentalists and data scientists. Thirdly, thanks to these methodological developments, I reconsider the binary definition of activity in the context of sleep, address some ambiguities in the literature regarding the effect of mating and address new questions about the endogenous determinism of sleep. Finally, I employ the ethoscope to perform, to my knowledge, for the first time in Drosophila, an automatic real-time sleep deprivation. The specific and parsimonious nature of this new treatment permitted a chronic depletion of sleep on a large population of flies. I show that, in stark contrast with the belief in the field, flies can perhaps survive with no sleep, challenging the notion that sleep is a universal vital need.