Emery Brown is a professor of computational neuroscience and health sciences and technology, with a joint appointment at MIT and Harvard University. He is also a professor of anesthesia at Harvard Medical School. MIT hide caption

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A woman with Alzheimer's disease walks in a corridor at a retirement house in Angervilliers, France, last month. Sebastien Bozon/AFP/Getty Images hide caption

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Charles Lotter is an operator of Tower Bridge in London and can work all night if a bridge lift is required. Sleep experts say that even people who routinely work night shifts will experience times when they get sleepy in the middle of the night. Peter Macdiarmid/Getty Images hide caption

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