Sleep seems like a perfect waste of time, declares a recent New York Times article. Why would our bodies evolve to spend close to one-third of our lives snoozing, it asks, when we could “instead be doing something useful or exciting? Something that would, as an added bonus, be less likely to get us killed” by predators?
“Sleep is such a dangerous thing to do when you’re out in the wild,” Maiken Nedergaard, a Danish biologist who has been leading research into sleep function at the University of Rochester’s medical school, told The Times. “It has to have a basic evolutional function. Otherwise it would have been eliminated. If sleep was just to remember what you did yesterday, that wouldn’t be important enough,” Dr. Nedergaard explains.
During sleep, your brain becomes a mental janitor
In a series of new studies published this fall in the journal Science, the Nedergaard lab may at last be shedding light on just what would be important enough. Sleep, it turns out, may play a crucial role in our brain’s physiological maintenance. As your body sleeps, your brain is clearing out all the junk that has accumulated as a result of your daily thinking, the article asserts. “Think about a fish tank,” says Dr. Nedergaard. “If you have a tank and no filter, the fish will eventually die.”
Until a few years ago, the prevailing model was based on the theory that the brain got rid of its waste by breaking it down and recycling it at an individual cell level. That didn’t make sense to Dr. Nedergaard, who instead, proposed a brain equivalent of the lymphatic system, a network of channels that cleared out toxins with watery cerebrospinal fluid. She called it the glymphatic system, because of its dependence on glial cells (supportive cells in the brain that maintain homeostasis and protect neurons) and its function as a sort of parallel lymphatic system.
As it happens, Dr. Nedergaard wasn’t the first to think of this. “It had been proposed about 100 years ago, but they didn’t have the tools to study it properly,” she says. Using today’s advanced microscopes and dyeing techniques, her team discovered that indeed, the brain’s fluid-filled area is dedicated to removing the cells’ daily waste.
A modern problem: we don’t sleep enough and therefore, our brains don’t have enough cleaning time
The figures are stark, according to The Times article. Approximately 80% of working adults suffer from sleep deprivation, and between 50 and 70 million people in the U.S. suffer from some form of chronic sleep disorder. When our sleep is disturbed, our cleaning system breaks down. What happens to our cognitive function when the trash piles up? At the extreme end, neurodegenerative diseases like Alzheimer’s and Parkinson’s.
Even at the relatively more benign end—the all-nighter or the extra-stressful week when you grabbed only a few hours a night—sleep deprivation, as everyone who has experienced it knows, impedes our ability to concentrate, pay attention to our environment and analyze information, the article explains. However, while our brains can recover quite readily from short-term sleep loss, chronic prolonged wakefulness and sleep disruption stresses the brain’s metabolism. The result is the degeneration of key neurons involved in alertness and proper cortical function and a buildup of proteins associated with aging and neural degeneration.
Dr. Sigrid Veasey at the University of Pennsylvania’s Center for Sleep and Circadian Neurobiology, told The Times that the research “very clearly shows that when we skip sleep, we may be doing irreparable damage to the brain, prematurely aging it or setting it up for heightened vulnerability to other insults.”
Good news: a new push to develop better methods for helping the brain clean itself
Better tests: If the main function of sleep is to take out our neural trash, this insight could eventually lead to a new understanding of both neurodegenerative diseases and age-related cognitive decline. By developing a diagnostic test to measure how well the glymphatic system functions, we could move one step closer to predicting someone’s risk of developing conditions like Alzheimer’s or other forms of dementia.
New ways to help us sleep better: Scientists are beginning to focus on developing earlier, more effective interventions to prevent cognitive decline. One solution? Anesthesia. Though too dangerous for daily use, anesthetics may be a way to improve sleep pharmacologically. In addition, a new generation of drug makers are working on ways to help the brain’s metabolism function as efficiently as possible. And finally, researchers are trying to simulate in the waking brain what is happening in the sleeping one, which could make a full night of sound sleep less necessary.
Whatever the future holds, one thing’s for certain: it’s not only important but actually crucial that you get your sleep!
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