Loretta Jackson gently stretches the hands of her sister, Shirlene English, to aid physical rehabilitation after Shirlene's brain aneurysm and stroke. Andrew Nixon/Capital Public Radio hide caption

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Rick and Marianne wash dishes together. She no longer remembers that he is her husband. Andrew Nixon/Capital Public Radio hide caption

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An Indian schoolgirl dressed as Telugu Talli poses for the camera during a celebration in Hyderabad, home to a study that seems to show the onset of dementia is delayed for people who speak more than one language. Noah Seelam/AFP/Getty Images hide caption

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University of Florida researcher Jennifer Stamps administers the peanut butter sniff test to a volunteer. Jesse S. Jones/University of Florida hide caption

itoggle caption Jesse S. Jones/University of Florida

Stressed out? Who isn't? Stress can cause physical changes in the brain that may be linked to Alzheimer's. iStockphoto.com hide caption

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Depression is common among old people, affecting up to 25 percent. iStockphoto.com hide caption

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An older man performs exercises in Mumbai, India. Research suggests that moderate physical exercise may be the best way to keep our brains healthy as we age. Rajesh Kumar Singh/AP hide caption

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A towel covers the face of a man in a geriatric day care facility of the German Red Cross at Villa Albrecht in Berlin. Carsten Koall/Getty Images hide caption

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Social worker Nuria Casulleres shows a portrait of Audrey Hepburn to elderly men during a memory activity at the Cuidem La Memoria elderly home in Barcelona, Spain, last August. The home specializes in Alzheimer's patients. David Ramos/Getty Images hide caption

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The flavonoids in coffee may have health benefits, but preventing stroke may not be one of them. iStockphoto.com hide caption

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A PET scan of the brain of a person with Alzheimer's disease. U.S. National Institute on Aging/via Wikimedia Commons hide caption

itoggle caption U.S. National Institute on Aging/via Wikimedia Commons

TimeSlips is a program based on the idea that storytelling can be therapeutic for people with dementia. Dick Blau/TimeSlips hide caption

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