TO SLEEP, PERCHANCE TO CLEAN
Scientists have long speculated that one of the functions of sleep is to restore and repair the brain, but whether this is a "core" purpose of sleep remains controversial. This year, researchers found direct experimental evidence that the mouse brain cleans itself during sleep, by expanding channels between neurons that allow an influx of cerebrospinal fluid. The fluid flushes out detritus such as amyloid proteins, which accumulate as plaques in Alzheimer's disease, twice as fast when mice are sleeping as when they are awake.
OUR MICROBES, OUR HEALTH
More than 100 trillion cells bearing three million genes live inside the human body. This year, researchers evaluating everything from malnutrition to cancer therapies came closer to pinning down several key roles for these cells and genes in determining how the body works. The results strengthen the case that personalized medicine will need to take our microbial guests into account to be effective. Many more details of how the bacteria can fuel or fight disease--particularly by influencing the immune system and inflammation--should emerge in the coming year.