Two soccer players collide on the field. A soldier in Afghanistan is thrown to the ground during a bomb explosion. A teen has an accident while riding her bike—and she isn't wearing her helmet. Each of these incidents can produce a traumatic brain injury (TBI). Of the 1.7 million Americans officially diagnosed with TBI each year, 52,000 die from their injuries. And that doesn't count all the unreported TBIs, which experts estimate range from about two to four million more incidents.

TBIs range from concussions to penetrating head injuries to life-threatening brain swelling and coma. And they have countless causes: war, sports, car and motorcycle accidents, falls, and physical violence. The aftereffects can be devastating, including compromised memory and concentration, loss of hearing, physical disabilities, depression, brain disorders, and, in the worst-case scenario, death.

Find out about the different types of TBIs, what causes them, and how they are diagnosed and treated. Along the way, you'll learn about National Hockey League player Derek Boogaard and U.S. Representative Gabby Giffords, both of whom sustained TBIs, with dramatically different outcomes. You'll also meet teens and young adults living with TBIs and the doctors who treat them. And you'll learn about amazing medical technologies that help victims recover and promise hope for the future.