How deep sleep keeps our brains intact

A patient undergoes a sleep study at the Washington University Sleep Medicine Center.
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When you live with dementia, your sleep breaks apart, the nights a strobe-lit blur, the grayed days lost to catnaps. Physicians — and families — have known this for years. But what no one realized, until landmark research at Washington University in 2009 set a series of studies in motion, was that fragmented sleep might be as much a cause as a consequence of dementia. And good sleep in middle age just might ward off a decline.