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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Andreas Fhager, a biomedical engineer at the Chalmers University of Technology in Sweden, adjusts the Strokefinder device on a test subject's head. Gunilla Brocker hide caption

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Sen. Mark Kirk, R-Ill., gets help entering the Capitol from Vice President Joe Biden (right) in January 2013, one year after suffering a stroke at age 52. Jewel Samad/AFP/Getty Images hide caption

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Aspirin has been prescribed for decades as a simple way to reduce heart disease risk, but doctors still aren't sure how it works. iStockphoto.com hide caption

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The cause of strokes in younger people remains largely a mystery. iStockphoto.com hide caption

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Insomnia, feeling isolated, and bursts of anger are symptoms of the anxiety disorder known as PTSD. iStockphoto.com hide caption

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