A recent article in Science revealed that the brain produces a fluid that actually washes out proteins from the brain that have been linked to Alzheimer's and dementia. I couldn't access the full article because the subscription fee is HIGH! But, here's a summary:
Taking Out the Trash
The purpose of sleep remains mysterious. Using state-of-the-art in vivo two-photon imaging to directly compare two arousal states in the same mouse, Xie et al. (p. 373; see the Perspective by Herculano-Houzel) found that metabolic waste products of neural activity were cleared out of the sleeping brain at a faster rate than during the awake state. This finding suggests a mechanistic explanation for how sleep serves a restorative function, in addition to its well-described effects on memory consolidation.
Abstract: The conservation of sleep across all animal species suggests that sleep serves a vital function. We here report that sleep has a critical function in ensuring metabolic homeostasis. Using real-time assessments of tetramethylammonium diffusion and two-photon imaging in live mice, we show that natural sleep or anesthesia are associated with a 60% increase in the interstitial space, resulting in a striking increase in convective exchange of cerebrospinal fluid with interstitial fluid. In turn, convective fluxes of interstitial fluid increased 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.
Here's a link to a summary article in Forbe's: http://www.forbes.com/sites/melaniehaiken/2013/10/18/sleep-detoxes-the-brain-new-research-suggests/
Research at Tuft's University suggests that study of glial cells' function during sleep could lead to breakthroughs in how to treat sleep disorders:
If you can't get enough info, here's a press release from http://www.bbc.co.uk/news/health-24567412
Hope you find this information useful.