Brain activity during sleep classically refers to circuit-specific oscillations, including slow waves, spindles, sharp-wave ripples or theta, that are nested in thalamocortical or hippocampus networks, respectively. However, the activity of other neuronal circuits is strongly modulated during sleep states. A major challenge is to determine the neural mechanisms underlying these activities and their functional implications in health and diseases. In this lecture, I will summarise our work on the dissection of the neural circuits underlying sleep-wake control, sleep oscillations and their relevance to brain plasticity associated with REM sleep, and discuss their relevance to motivated behaviours and emotional processing.