Clues to the functions of mammalian sleep

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Nature 437, 1264-1271 (27 October 2005) | doi:10.1038/nature04285; Published online 26 October 2005

Clues to the functions of mammalian sleep

Jerome M. Siegel1

Abstract
The functions of mammalian sleep remain unclear. Most theories suggest a role for non-rapid eye movement (NREM) sleep in energy conservation and in nervous system recuperation. Theories of REM sleep have suggested a role for this state in periodic brain activation during sleep, in localized recuperative processes and in emotional regulation. Across mammals, the amount and nature of sleep are correlated with age, body size and ecological variables, such as whether the animals live in a terrestrial or an aquatic environment, their diet and the safety of their sleeping site. Sleep may be an efficient time for the completion of a number of functions, but variations in sleep expression indicate that these functions may differ across species.

1. Neurobiology Research 151A3, VA GLAHS Sepulveda, Department of Psychiatry and Brain Research Institute, UCLA School of Medicine, North Hills, California 91343, USA.
Email: JSiegel@ucla.edu