Objective
Human adaptation to modern 24-h society is constrained by dominant endogenous periodicities in physiology and behaviour. These rhythms, including the sleep-wake cycle, are generated in the brain's suprachiasmatic nuclei (SCN). Their understanding has major biomedical impact in the combat of sleep disorders, control of fatigue and risk, adjustment to shift work, timing of drug therapies. Big strides are being made in unravelling the physiological and molecular basis of circadian rhythms. Building on these advances we combine molecular, brain and behaviour studies to elucidate the control of sleep-wakefulness in mouse models and humans. Human studies focus on screening for phase variations in sleep-wake rhythms and their molecular characterization. Mouse strains with genetically modified circadian genes are exploited to characterize the mechanism underlying SCN oscillations and establish time-specific neuroanatomical mapping of circadian gene expression throughout the brain. Complementary expertise allows the assembly of a coherent picture of generation and synchronization of neuronal clocks involved in adaptation to a rotating planet.