Why do we sleep? It is a question that has long puzzled scientists and philosophers alike. While the ancient Greeks saw sleep as a doorway to the divine, scientists and biologists see it as an invitation to be devoured by nocturnal predators. A new study – appearing today in the journal Science – may provide the answer: when we sleep our brain ‘takes out the trash.’
The findings are one in a series of discoveries that have revolutionized our understanding of how the brain deals with the by-products of cellular activity. The body’s normal waste removal process – called the lymphatic system – does not extend to our brains. This is because the brain essentially maintains its own closed “ecosystem.” However, as any student of biology knows waste removal is a critical biological function. In the brain, the unchecked accumulation of proteins such as beta-amyloid can lead to Alzheimer’s disease.
Last year, URMC researchers – led by Maiken Nedergaard, M.D., D.M.Sc. – revealed that the brain has its own waste removal system consisting of a plumbing system that piggybacks on the brain’s blood circulation system and uses cerebral spinal fluid to wash away waste. The studies were conducted in mice, whose brains are remarkably similar to humans.
The study out today shows that this system is 10-times more active during sleep and more effective at removing beta-amyloid. This finding has led researchers to speculate that the brain essentially has two functional states – awake and processing information about our surroundings and asleep and cleaning away the material that neurons generate during their normal activity.
Another startling finding was that the brain’s cells “shrink” during sleep – by as much as 60 percent – which allows the cerebral spinal fluid to more easily flow between the cells and flush away waste.
You can read more about the Science paper here.
Mark Michaud |
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