It happened in a fraction of a second.
On Jan. 29, 2006, a roadside bomb detonated next to the vehicle carrying ABC News anchor Bob Woodruff in Iraq. The shock wave from the explosion propelled jagged shrapnel and rock, traveling at a deadly velocity, toward his head.
In less time than it takes to read this sentence, his brain was forever changed.
Woodruff awoke more than a month later, only to begin a long road to recovery. His journey is one that is shared by an estimated 80,000 to 90,000 Americans each year who suffer traumatic brain injury, or TBI.
While at least some degree of recovery is possible for many of these patients, the progress back to the people they once were is gradual and uncertain.
And many do not make it back.
Mark Ashley is president of the Centre for Neuro Skills and is on the board of directors of the Brain Injury Association of America. He says the way that a traumatic brain injury progresses relates to the brain's layered structure.
Running through these layers is an intricate system of delicate nerves and blood vessels, all crucial to the brain's proper functioning.
When the head is hit with a great deal of force, Ashley says, "Each of the different layers -- because they are of different densities and different weights -- travel at different speeds."
Thus, Ashley says that in many ways, the effect of such a force can be compared to that seen in a city during an earthquake -- except that instead of pipes and underground cables, the connections being sheared are the fragile connections of nerves and vessels between the layers of the brain.
Most vulnerable to these forces is the network of tissues that connect the right side of the brain to the left -- what Ashley calls the "wires" that allow the connection of one part of the brain to the other.
When a trauma, such as that created by an explosion, disrupts this living switchboard, the effects on the brain can be drastic.
"As these wires become detached, now we end up with widespread damage throughout the brain," Ashley said.
In the initial days and weeks after a traumatic brain injury, the first hurdle a patient must face is the simple act of survival.
While a patient with a brain injury, such as a stroke, may be medically stable within 24 hours to 48 hours, Ashley says, a person with moderate to severe brain injuries "may be critically ill for days or weeks."
Kit Callahan has a firsthand familiarity with such an experience.
Callahan sustained a traumatic brain injury when he was assaulted in 1993. The assault left him with massive head injuries, and he remained in a coma for weeks.
When he finally awoke, he faced a new challenge: learning how to communicate and move his body now that his brain had suffered irreparable damage.
"The hardest part for me was just learning to walk and talk again," he said. "My speech is obviously no longer what it used to be."
"If you had known me before, you would have known I have a great singing voice," he said.
The comment is a self-effacing joke -- a feat requiring brainpower that would have been impossible to muster during the early phases of his recovery, when even simple communication was impossible.
"Saving a patient's life is only just the beginning," said psychiatrist Gregory O'Shanick, medical director of the Center for Neurorehabilitation Services in Midlothian, Va.