Deciphering what happened in an explosion is tricky.
"The very nature of sustaining the brain injury means you've lost memory or lost consciousness around the time of the injury," said Kathy Helmick, deputy director of the National Defense and Veterans Brain Injury Center in Washington.
Unlike football collisions - where teammates, spectators and perhaps millions of TV viewers can see a concussion happen in real time - explosions often leave few reliable witnesses. Many survivors who might tell the tale can't remember, either.
Researchers, including some at the Johns Hopkins University, are studying the mechanisms by which blast waves transmit energy through the skull, eyes and ears to the brain itself.
Whatever the cause, brain injuries treated at the VA and military hospitals share common symptoms.
"There's an inability to hold something in your head and work on it," said Cernich. "If I gave you a math problem and said, 'What's four times 25?', you'd have to hold that equation in your head, perform the equation and spit out an answer."
The same principle applies to simple tasks, such as walking into a room and remembering why you went there, she said. Most people have similar lapses from time to time, but not nearly to the extent of those with brain injuries.
Many veterans who suffered brain injuries also have post-traumatic stress disorder, which can cause similar symptoms - along with flashbacks and a recurring fear that a catastrophe is going to happen again.
Irrepressibly optimistic, Jason Ehrhart says he doesn't dwell on the past or fear for the future. Of his accident, Ehrhart vaguely recalls that he was blasted out of his vehicle while rolling through Baghdad in December 2005.
"Then, the next thing you know, I was flying high in the air," he said in a description that his mother believes he heard from others. "I was like Superman."
The blast threw him 25 feet and killed three soldiers and a bomb-sniffing dog. Ehrhart woke up three months later in a Texas military hospital.
At first, he had trouble learning to swallow again, a reflex he eventually regained by chewing sweetened gum that triggered salivation and the myriad muscle contractions that follow. He doesn't have trouble finding words, but sometimes he speaks too fast and utters profanities in the wrong company.
"Everyone has filters that have been programmed since childhood," said his stepfather, Michael Estes. "His filter has been removed."
