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Neural Plasticity
Volume 2012 (2012), Article ID 415250, 12 pages
Review Article

Time to Be SHY? Some Comments on Sleep and Synaptic Homeostasis

Department of Psychiatry, University of Wisconsin, Madison 6001 Research Park Boulevard, Madison, WI 53719, USA

Received 26 January 2012; Accepted 13 February 2012

Academic Editor: Alfredo Fontanini

Copyright © 2012 Giulio Tononi and Chiara Cirelli. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Sleep must serve an essential, universal function, one that offsets the risk of being disconnected from the environment. The synaptic homeostasis hypothesis (SHY) is an attempt to identify this essential function. Its core claim is that sleep is needed to reestablish synaptic homeostasis, which is challenged by the remarkable plasticity of the brain. In other words, sleep is “the price we pay for plasticity.” In this issue, M. G. Frank reviewed several aspects of the hypothesis and raised several issues. The comments below provide a brief summary of the motivations underlying SHY and clarify that SHY is a hypothesis not about specific mechanisms, but about a universal, essential function of sleep. This function is the preservation of synaptic homeostasis in the face of a systematic bias toward a net increase in synaptic strength—a challenge that is posed by learning during adult wake, and by massive synaptogenesis during development.