Since his college days, New England Revolution forward Taylor Twellman has had seven diagnosed concussions. Given all the headers and hits over his career, he's wondering if that number might be drastically higher.

Twellman still deals with the effects of a concussion he sustained during a collision with a goalkeeper two years ago, one that possibly cost him a shot at making the U.S. World Cup team and cut short his 2010 season after going on injured reserve in late June.

Now he's volunteered to join a Boston University medical school program in which researchers are trying to better understand the long-term effects of repeated concussions. He's one of 300 athletes in just the last two years who have agreed to undergo a battery of annual tests and donate their brain after death.

"It's not hard [to donate] in that you want to help people down the road," Twellman told The Associated Press in a telephone interview. "But it is hard since they want your brain because it's been damaged."

The athlete registry is the work of the university's Center for the Study of Traumatic Encephalopathy, a collaborative venture between BU Medical School and the Sports Legacy Institute that's addressing what it calls the "concussion crisis" in sports. The group has been at the forefront of research into head trauma in sports and received a $1 million gift from the NFL, which it has pushed for better treatment of concussions.

In addition to the athlete volunteers, the families of 40 deceased players have donated brain and spinal column tissue of their loved ones to the center. The material has been studied to see if repetitive head injuries possibly led to a degenerative disease known as chronic traumatic encephalopathy.

Chris Nowinski, the co-founder of the Sports Legacy Institute, leads the charge to round up donors.