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Does Sleep Start the Dishwasher in Our Brains?

Sleep is critical for clearing the brain of unwanted waste

I don’t know about you but the last task before I head to bed is to start the dishwasher. It’s a critical ritual for good reason- basically my two year-old dirties a ton of dishes. The dishwasher is a marvelous contraption that wipes the slate clean, so to speak, from the mess of the day before. Remarkably, new research suggests that the sleeping may do the very same thing for our brains.

In a recent study, researchers used mice to understand how sleep affects the ability of the brain to “wash away” the toxins from the day (Xie et al., 2013). Essentially, waste materials accumulate in the brain as byproducts of everyday brain activity. Cerebrospinal fluid (CSF), which bathes the brain, gathers up these waste products and flushes them out of the system. How does this happen? Well, there is space between brain cells, known as the interstitial space. It is in this space that CSF interacts with interstitial fluid (ISF) to remove these unwanted byproducts. The larger the interstitial space the better able CSF interacts with this ISF- and with that you get better, more effective brain cleaning. The researchers used sophisticated measures of diffusion and imaging to see how this process differed in awake vs. naturally sleeping vs. anesthetized (unnatural but nevertheless sleeping) mice. They found that both the sleeping and anesthetized mice showed dramatic increases in their amount of interstitial space--- 60% more space. As you might expect, this increase had important effects on byproduct clearance, namely on the clearance of ß-amyloid (Aß). You may have heard of Aß as it is the main component of deposits found in the brains of those who have Alzheimer’s disease. This study found that Aß was cleared from the brain twice as fast in sleeping mice (naturally or anesthetized) compared to waking mice.

Why is this work so important?

First, those interested in sleep research have struggled for decades to understand why we sleep at all. Of course, sleep is without question restorative, both for body and mind, and conserved across species. The fact that all species sleep suggests a possible universal benefit- but what? These findings raise the possibility that clearance of metabolic waste may be that very benefit. Second, this work could have important implications for understanding neurodegenerative conditions, such as Alzheimer’s disease. For instance, a recent study of normally aging adults found that those who reported sleeping fewer hours had higher levels of Aß in their brains when compared to similarly aged individuals who slept longer (Spira et al., 2013). Could this newfound process observed in mice explain these findings in humans? Only time will tell.

Bottom line. Sleep appears to play an important role in clearing your brain of metabolic waste, including proteins related to neurodegenerative diseases of aging. Not only is sleep good for your well-being, it appears to start that dishwasher in your brain. No pre-soaking required. Amazing.

Check out the original research to learn more:

Xie et al., 2013. Sleep drives metabolic clearance from the adult brain. Science, 342, 373-377.

Spira et al., 2013. Self-reported sleep and Beta-Amyloid deposition in community-dwelling older adults. JAMA Neurology, published online October 21, 2013.