Thomas Jones, a retired running back who played for five teams in 12 NFL seasons, has decided to donate his brain, upon his death, to the Sports Legacy Institute to be studied for evidence of chronic traumatic encephalopathy (CTE). Jones said he has no idea how many concussions he sustained, but he's concerned with what they could mean for his future.

"Honestly, like I couldn't give you a number because you just play with them," Jones said. "You can't know; nobody does. I think the guys counting the concussions were the ones that got knocked out."

The Sports Legacy Institute won't confirm individual donations, but a spokesperson said that more than 600 living athletes have decided to donate their brains to be studied. Of 34 neural tissue samples from NFL players, 33 had evidence of CTE. Jones said he can only guess at what has happened to his brain after 20 years of games and practices -- and numerous "baby concussions" -- through his NFL, college and high school career.

"It's like taking a fresh, ripe apple and tapping it with your thumb over and over again," Jones said.

Jones is in the editing process of a documentary series, "The NFL: The Gift or the Curse?" The first of six planned episodes produced by Jones' company, Independently Major Entertainment Films, deals with concussions and suicide. He interviewed Ann McKee and Chris Nowinski, co-directors of the Center for the Study of Traumatic Encephalopathy at Boston University.

Jones decided to make his donation after conducting interviews for the project.

Last week, Junior Seau's family revealed that his brain showed evidence of CTE when he committed suicide last year. This generation of players is the first to play with concrete evidence that they could be compromising not-too-distant futures by playing professional football.

In the documentary, Jones also interviewed former defensive end Adewale Ogunleye, who was drafted by the Dolphins in 2000. Ogunleye sees ominous signs in what might just be everyday forgetfulness.

"Somebody might tell me their name; I don't remember it right away," Ogunleye said. "Now I kind of laugh it off, but when stuff like that happens, I'll be like, 'Damn, I hope these concussions don't come back to haunt us in the end.' And if they do, I just pray someone is there to help me through the tough times that may come."

In the rough cut, Ogunleye then puts his face in his hands. Jones comes over and puts his arm on Ogunleye's shoulder.

These issues are personal for NFL players. Jones uses the example of Dave Duerson's suicide in February 2012.

"His suicide, you see it on TV and it's just news," Jones said. "But to us, it's more than that."

Jones envisions the series as the players speaking directly to the fans about the pitfalls of playing in the NFL. He understands that many people see attaining the dream of playing in the NFL as a dream come true, but he wants to show what it looks like through the eyes of the men who reached that goal.

"The fans look at it as money," Jones said, "but once you've bought everything you want, you realize there is more you want out of life."

The series also will focus on issues such as domestic violence and financial pressures. Jones is talking with possible distributors for the project.