Varsity football captain Nahshon Ellerbe is a senior at Trinity Christian Academy in Addison, Texas. Jeffrey McWhorter/Trinity Christian Academy hide caption

itoggle caption Jeffrey McWhorter/Trinity Christian Academy

High school athlete Graham Hill, number 50, suffered a concussion in 2013 while playing football at Trinity Christian Academy, in Addison, Texas. Courtesy of Jeffrey McWhorter hide caption

itoggle caption Courtesy of Jeffrey McWhorter

For the past 34 years, the William Grant Still Arts Center has held a Black Doll Show to showcase diverse dolls for children. The exhibit features dolls submitted by artists and collectors from around the country. Priska Neely/NPR hide caption

itoggle caption Priska Neely/NPR

A polar bear walks in the Arctic National Wildlife Refuge.The Obama administration is proposing new protections in the region that would ban mining and drilling. Subhankar Banerjee/AP hide caption

itoggle caption Subhankar Banerjee/AP

When he was 59 years old, Greg O'Brien was diagnosed with early-onset Alzheimer's disease. Five years later, he is speaking publicly about his experience, even as his symptoms worsen. Courtesy of Greg O'Brien hide caption

itoggle caption Courtesy of Greg O'Brien