While the wars in Iraq and Afghanistan continue, the Vanderbilt Brain Institute fights a new battle against an epidemic of soldiers with brain injuries.
Thousands of troops have been diagnosed with traumatic brain injury since the wars began. These blast-caused head injuries differ greatly from the car crash injuries doctors usually see.
People with TBI have frequent headaches, dizziness, and trouble concentrating and sleeping. They may be depressed, irritable, confused, easily provoked or distracted. Speech or vision can be impaired.
"This is the signature injury of this war," said Dr. Sandy Schneider, director of the brain injury rehabilitation program at Vanderbilt. "This type of TBI injury is very different from anything me or my staff have seen over the years. It is something we are still learning a lot about."
Some soldiers who seek treatment have been misdiagnosed with personality disorders.
"It's the so-called invisible injury. It's when the patient and his or her family knows something isn't right, but they can't pinpoint the symptoms together," said Dr. David Twillie, chief medical director for the Fort Campbell military base in Kentucky.
Sgt. Major Allard, an army career infantryman from Stonebridge, Mass., who is being treated at Vanderbilt, said his wife and commanding officer noticed something was wrong and prompted him to see a doctor.
He was diagnosed with mild TBI. The doctors told him he would not be able to return to combat right away and would need to seek immediate treatment, he said.
Almost all TBI cases treated at Vanderbilt are mild, and most patients recover within six months to a year.
But as more and more troops have returned from war with some form of brain injury, the center has struggled to meet the need.
"The program at Vanderbilt has already had to add seven new staff members," Schneider said. "We need more staff members; however, professionals that deal with these kind of injuries traditionally take a long time to hire, not to mention the security and background checks needed to work with our wounded warriors."
And cases can be complicated by a number of other factors. Some symptoms associated with TBI are also associated with post-traumatic stress disorder. TBI can effectively block PTSD by hindering a soldier's emotional recovery.
As the TBI treatment progresses, the emotions of war of come back, and soldiers begin to
show signs of PTSD, Schneider said.
And many troops get no care at all. Some are sent back to fight with their brain injuries undetected. U.S. soldiers are protected so well by the armor from neck down that improvised-explosive devices do not leave any visible injuries.
Even those who are treated successfully may still grapple with the symptoms throughout their lives.
"The one thing we must remember is we don't know what the long term effects are," Schneider said.
Allard said he plans to stay in the Army and return to war when he recovers.
He has been assigned to lead the Wounded Warriors transition unit at Ft. Campbell while he is recovering. The unit helps transition soldiers into recovery and beyond, whether they return to the war or leave the army and enter civilian life.
"This has been a tremendous opportunity to care for our wounded warriors, but I plan to return to my unit and the war," Allard said.
Schneider said she keeps the soldiers in the front of her mind.
"The war doesn't stop here. We have a duty to give our wounded warriors the best care long-term, and that's what the Vanderbilt program plans to do," she said.

-The Associated Press contributed reporting to this article.