The brain of former NFL star Junior Seau, who committed suicide last year, showed signs of the kind of neurodegenerative disease associated with repetitive head trauma. Elsa/Getty Images hide caption

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Baltimore Ravens linebacker Ray Lewis speaks at a news conference in New Orleans on Monday. The Ravens face the San Francisco 49ers in Super Bowl XLVII on Sunday. It will be Lewis' last game. Patrick Semansky/AP hide caption

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Echolocation is second nature to animals such as bats and dolphins. Can humans also find their way using sound as a tool? Ian Waldie/Getty Images hide caption

itoggle caption Ian Waldie/Getty Images