In an article titled, “Sleep Drives Metabolite Clearance from the Adult Brain”, published in Science  on 18th October   2013: (Vol. 342), the lead author Maiken Nedergaard and 12 of his associates affiliated to the Department of Neurosurgery, University of Rochester Medical Center, Rochester, NY and Department of Neuroscience and Physiology, Langone Medical Center, New York University, describe that  sleep serves a vital function in all animals  ensuring metabolic homeostasis. Using real-time assessments of tetramethylammonium diffusion and two-photon imaging in live mice, they have  shown that natural sleep is associated with a 60% increase in the interstitial space.  In turn, convective fluxes of interstitial fluid increases the rate of β-amyloid clearance during sleep. Thus, the restorative function of sleep may be a consequence of the enhanced removal of potentially neurotoxic waste products that accumulate in the awake central nervous system.  The authors  have shown that sleep ensures metabolic homeostasis.