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."
To some extent, his lack of inhibition has an endearing quality. As his parents say, if you ask him a question, you'd better expect an honest answer.
Dr. Benjamin Yorkoff, his primary care physician at the Baltimore VA, said his patient has benefited greatly from the speech therapy, psychotherapy and other services he receives at Humanim, a private rehabilitation center in Columbia. The VA made the referral and pays for much of the care.
"Now you can take Jason out in public and he's more appropriate," said Yorkoff, who first saw Ehrhart in a nearly vegetative state at the Richmond VA. "There was a time when you could barely take him into a public arena because he didn't have the social skills."
Injured in October 2006, Perry receives occupational and psychotherapy at the veterans hospital in Perry Point. He wants to become a preacher but is not currently working, owing in part to his problems with short-term memory.
"My wife gives me things to do, and I'll remember some of the things but not all of them," he said.
She started making lists for him but he would often forget that he had them. More recently, he has found that entering tasks in a hand-held device is helpful - and not just as a reminder to do things. Somehow, he said, the act of recording things makes them easier to remember.
Perry has to cope with the fact that many people he meets don't realize he has suffered a brain injury, said Cernich. That's because his head looks unscathed.
"Some people you meet may never be able to see the injury," she said, referring to Perry. "But it's just as valid an injury as breaking your elbow or having an amputation."
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