About twice a year, statistics suggest, a pilot somewhere in the world — usually flying alone — deliberately crashes a plane. The Germanwing flight downed last week may be one such case. But most people who fit the psychological profile of the pilots in these very rare events never have problems while flying. Patrik Stollarz/AFP/Getty Images hide caption

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When combined with results of other neurological tests, and in the context of a thorough medical history, atrophy of the brain (shown here in an MRI scan) sometimes indicates Alzheimer's. Simon Fraser/Science Source hide caption

itoggle caption Simon Fraser/Science Source

Laury Sacks and her husband, Eric. The actress and writer developed frontotemporal dementia in her late 40s and died in 2008 at age 52. Courtesy of Eric Sacks hide caption

itoggle caption Courtesy of Eric Sacks

Jonathan Keleher talks with a colleague, Rafael Wainhaus, at work. Keleher was born without a cerebellum, but his brain has developed work-arounds for solving problems of balance and abstract thought. Ellen Webber for NPR hide caption

itoggle caption Ellen Webber for NPR

Jonathan Keleher is one of a handful of people who have lived their entire lives without a cerebellum. Ellen Webber for NPR hide caption

itoggle caption Ellen Webber for NPR

Benjamin Rush, a physician and one of the signers of the Declaration of Independence, invented the rotational chair as a treatment for psychotic patients. He believed the chair helped improve circulation to the mentally ill brain. U.S. National Library of Medicine/Courtesy of Little Brown and Company hide caption

itoggle caption U.S. National Library of Medicine/Courtesy of Little Brown and Company

Prion protein can be infectious, spreading from cell to cell in the brain. Here four nerve cells in a mouse illustrate how infectious prion protein moves within cells along neurites — wire-like connections the nerve cells use for communicating with adjacent cells. Science Source hide caption

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Boys wait in line to make a phone call at the U.S. Customs and Border Protection Nogales Placement Center in Arizona in June. Many of the minors who arrived from Central America last year are now awaiting court hearings to determine if they can stay in the U.S. Ross D. Franklin/Pool/Getty Images hide caption

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