Sleep, on the face of it, appears to be a complete waste of our precious time. Why has our body evolved such a strange mechanism? Why would we let nearly a third of our lives go by without using it for something useful or fun? Back in the ancient days when our ancestors lived in tropical and subtropical savannas, sleep undoubtedly increased the risk of death, but why – why is sleep so essential to us? We have previously learned that sleep is essential for memory formation and consolidation, and that it plays a central role in the formation of new neural connections and in the repair of old ones. But.
“If sleep could only help you remember what you did yesterday, it wouldn’t be so important,” explains Danish biologist Dr. Nedjard. In a new series of studies published in the journal Science, Nidjad’s lab may have finally found a key clue to answering the question of sleep’s importance. It turns out that sleep plays an important role in the “maintenance” of the physiological level of the brain. When your body falls asleep, your brain still dutifully acts as your “mental janitor,” cleaning up the “junk” that accumulates during your daytime thinking activities for you. After a series of new studies on mice, her team found this to be true: while the mouse brain was asleep or under anesthesia, it was busy clearing out the junk that had accumulated during waking hours. In the mouse brain, tissue gaps account for about 14 percent of the total brain volume, a smaller percentage than in our brains. But Dr. Nidjad found that when mice are asleep, the volume of the tissue gap can expand to more than 20 percent of total brain volume. This not only allows brain crest fluid to flow more freely, but also allows it to reach deeper parts of the brain. In the waking brain, cerebral crest fluid can only flow along the surface of the brain. To be precise, the flow of brain crest fluid during wakefulness is only 5 percent of that during sleep, while the brain can clear waste up to twice as fast during sleep as during wakefulness. “When the mice are awake, we barely observe any brain crest fluid flow into the brain; but when the mice are anesthetized, brain crest fluid begins to flow. The difference was so great that I kept worrying if something was wrong,” said Dr. Nidjad. Modern society is increasingly unable to guarantee the time necessary for our brains to perform these cleanup tasks. The following figures are indicative of this stark fact: About 80 percent of adult working adults suffer from some degree of sleep deprivation. According to the National Sleep Foundation, adults should get seven to nine hours of sleep a day. On average, people today get one to two hours less sleep per night than they did 50 to 100 years ago, and 38 minutes less sleep on weekday nights than they did 10 years ago. In the United States, approximately 50 to 70 million people suffer from some form of chronic sleep disorder. For whatever reason, whenever sleep is disturbed, our purging systems fail. How does our cognitive function suffer when brain junk builds up? In the most extreme cases, it can lead to an accelerated course of neurodegenerative diseases such as Alzheimer’s and Parkinson’s disease.