Every year traumatic brain injury (TBI) causes 50,000 deaths and 80,000 cases of long-term disability in the United States, according to the Centers for Disease Control and Prevention. An estimated 5.3 million Americans (some 2 percent of the population) live with long-term disabilities due to brain injury.

Yet much about brain injuries remains unknown. Despite decades of research, no treatments yet target the underlying pathophysio­logical cause of progressive brain damage. For patients so severely injured that they are in a minimally conscious state, medical knowledge is particularly lacking; in such cases, we are just beginning to understand the damage and the possibility of treatment (see "Raising Consciousness").