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Rough night? Depending on specific tweaks to their genes, some fruit flies have trouble falling asleep, and others can't stay asleep. Getting too little shut-eye hurts their memory. David M. Phillips/Science Source hide caption

itoggle caption David M. Phillips/Science Source
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Renowned British neurologist and author Oliver Sacks, pictured in London in 1983, died Sunday of cancer. He was 82. United News/Popperfoto/Getty Images hide caption

itoggle caption United News/Popperfoto/Getty Images

Michael Arnott, of Cambridge, Mass., says he used to have trouble staying awake on long drives. Sleep specialists discovered he has obstructive sleep apnea, though not for the most common reasons — he isn't overweight, and doesn't smoke or take sedatives. M. Scott Brauer for NPR hide caption

itoggle caption M. Scott Brauer for NPR

A nanosecond pulsed laser beam starts the photoacoustic imaging process. Geoff Story/Courtesy of Washington University in St. Louis hide caption

itoggle caption Geoff Story/Courtesy of Washington University in St. Louis

Giedre (left) and Tal Cohen in March 2013, while Giedre was still healthy. Since then, she's begun having symptoms of Alzheimer's disease. In Giedre's case, the illness is tied to a rare genetic mutation she inherited. Courtesy of Tal Cohen hide caption

itoggle caption Courtesy of Tal Cohen

Women with mild cognitive impairment, which can be a precursor to Alzheimer's, tend to decline faster than men. Lizzie Roberts/Getty Images/Ikon Images hide caption

itoggle caption Lizzie Roberts/Getty Images/Ikon Images

In this colorized image of a brain cell from a person with Alzheimer's, the red tangle in the yellow cell body is a toxic tangle of misfolded "tau" proteins, adjacent to the cell's green nucleus. Thomas Deerinck/NCMIR/Science Source hide caption

itoggle caption Thomas Deerinck/NCMIR/Science Source

"Shout, shout, let it all out. These are the things I can do without." Simone Golob/Corbis hide caption

itoggle caption Simone Golob/Corbis
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