[Why do we sleep? Contributions from animal research]

Despite the almost ubiquitous presence of sleep and the sleep stages nonREM and REM sleep in mammals and birds, the functions of sleep still remain elusive. Several promising approaches may shed light on this problem. Thus investigation of sleep-like states such as hibernation and torpor have shown that these states are more similar to sleep deprivation than to sleep. Furthermore, sleep-like states, which are homeostatically compensated for after rest deprivation have been found in Drosophila. These results allow to search for genes and gene products which change as a function of the vigilance states in these more simpler organisms. Thereafter, homologous genes can be investigated in mice.