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Published online on January 10, 2007, 10.1073/pnas.0610080104
PNAS | January 16, 2007 | vol. 104 | no. 3 | 1051-1056


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BIOLOGICAL SCIENCES / PHYSIOLOGY
A quantitative, theoretical framework for understanding mammalian sleep

Van M. Savage*,{dagger},{ddagger},§,¶, and Geoffrey B. West*,{dagger}

*Santa Fe Institute, 1399 Hyde Park Road, Santa Fe, NM 87501; {dagger}Los Alamos National Laboratory, MSB285, Los Alamos, NM 87545; {ddagger}Bauer Laboratory, Harvard University, 7 Divinity Avenue, Cambridge, MA 02138; and §Department of Systems Biology, Harvard Medical School, 200 Longwood Avenue, Boston, MA 02115

Communicated by Murray Gell-Mann, Santa Fe Institute, Santa Fe, NM, November 20, 2006 (received for review September 1, 2006)

Sleep is one of the most noticeable and widespread phenomena occurring in multicellular animals. Nevertheless, no consensus for a theory of its origins has emerged. In particular, no explicit, quantitative theory exists that elucidates or distinguishes between the myriad hypotheses proposed for sleep. Here, we develop a general, quantitative theory for mammalian sleep that relates many of its fundamental parameters to metabolic rate and body size. Several mechanisms suggested for the function of sleep can be placed in this framework, e.g., cellular repair of damage caused by metabolic processes as well as cortical reorganization to process sensory input. Our theory leads to predictions for sleep time, sleep cycle time, and rapid eye movement time as functions of body and brain mass, and it explains, for example, why mice sleep {approx}14 hours per day relative to the 3.5 hours per day that elephants sleep. Data for 96 species of mammals, spanning six orders of magnitude in body size, are consistent with these predictions and provide strong evidence that time scales for sleep are set by the brain's, not the whole-body, metabolic rate.

allometric scaling | brain | cellular repair | metabolic rate | sleep times

Author contributions: V.M.S. and G.B.W. designed research; V.M.S. and G.B.W. performed research; V.M.S. analyzed data; and V.M.S. and G.B.W. wrote the paper.

The authors declare no conflict of interest.

This article contains supporting information online at www.pnas.org/cgi/content/full/0610080104/DC1.

To whom correspondence should be addressed. E-mail: van_savage{at}hms.harvard.edu

© 2007 by The National Academy of Sciences of the USA


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V. M. Savage, A. P. Allen, J. H. Brown, J. F. Gillooly, A. B. Herman, W. H. Woodruff, and G. B. West
Scaling of number, size, and metabolic rate of cells with body size in mammals
PNAS, March 13, 2007; 104(11): 4718 - 4723.
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