Shortly after he'd been exposed to not one — but several — improvised explosive devices (IEDs), Chris Riga realized something wasn't right.

"The first time I noticed, we had been through multiple IED strikes within a week period years ago in Afghanistan. And, unfortunately, I was at a memorial ceremony, and I couldn't keep my balance after standing up for about two minutes," Riga says. "I'd have to grab onto something or lean against something to be able to stand for that amount of time."

Riga in his office at the Northampton VA Medical Center. (Jesse Costa/WBUR)

Riga served several tours in Afghanistan from 2001 to 2014, eventually commanding all U.S. special forces there. During his 29 years in the Army's 82nd Airborne, Rangers and 3rd and 7th Special Forces groups, he also served in Africa and Iraq.

"We were always either preparing for combat or deployed in combat," Riga says. "Blasts and exposures were a daily incident. So I've always been interested in what effect that has on your brain, your body, and everything else."

After the invasion of Iraq, the VA and Department of Defense were confronted between 2004 and 2005 with a large number of traumatic brain injuries (TBI) and concussions from IEDs. In previous wars, people died from other injuries. Their survival rate from those injuries had improved.

Veterans Administration researchers in Boston were tasked with understanding the long-term effects of TBI. They decided to cast a wide net to look at variety of symptoms, such as post-traumatic stress disorder (PTSD), alcohol abuse and sleep problems.

It's now the most comprehensive study to date of blast injuries on post-9/11 veterans. A record number of veterans from around the country have enrolled in the study to find out what blast exposure has done to them.

"We don't only look at the military service period," says Regina McGlinchey, one the study's co-directors. "We look at what happened to these people when they were younger, before they were in the military, so we capture things like rock wars and sledding incidences when they were growing up--"

"Sports injuries and bar fights, and the whole gamut," interjects Bill Milberg, the study's other co-director.

"The whole nine yards," says McGlinchey, laughing.

McGlinchey, Milberg and other researchers at the Boston VA found exposure to blasts also resulted in changes to brain function and brain structure.

McGlinchey says they are not trying to understand just PTSD, or just TBI.

"It's like: What does war do to an entire person?" McGlinchey says.