If the National Football League had not changed the way it identified and treated concussions in the last three years, the argument could be made that the Green Bay Packers may have never won Super Bowl XLV.

It wasn't long ago that major head trauma was labeled by coaches and players as "a dinger" or getting their "bell rung." It was more of an induction into a special fraternity than a long-term health concern, one that can lead to problems with movement, learning and speaking.

In the middle of the 2009 season, Thom Mayer, the medical director of the NFL Players Association, and other union leaders set out to "change the culture" of the league with better tests to identify concussions and better treatment when they occurred.

A year later, Packers quarterback Aaron Rodgers suffered the first two concussions of his life.

"One was clearly recognized in the Washington Redskins game and everybody knew he had a concussion," Mayer said. "The second was a few weeks later, in that Lions game. It was not recognized."

One of the things Mayer had introduced to the NFL was a concussion identity strategy borrowed from the U.S. military, the "battle buddy" concept. Soldiers are asked to pair up and check on one another after explosions or other traumatic events. In Rodgers' case, his battle buddy was wide receiver Donald Driver.

"Driver went over to Rodgers and said, 'Dude, what's up with the snap count?' " Mayer said. "Driver is the one who went over to the trainers and said, 'Hey, this guy ain't right, get him out of there.' "

Rodgers exited the Lions game, sat out the next week against New England, got healthy and came back to win every game the rest of the way - ending with the Super Bowl championship.

"That probably changed the outcome of Super Bowl XLV," Mayer said. "If Rodgers would have stayed in the Lions game, concussed, the chances of him getting concussed again are infinitely higher."

There is no greater issue facing the NFL right now than concussions. In fact, three starting quarterbacks were knocked out of games on Nov. 11 - Philadelphia's Michael Vick, San Francisco's Alex Smith and Chicago's Jay Cutler.

With scientists and doctors uncovering stunning cause-and-effect results on their autopsy tables, with thousands of former players joining class-action lawsuits, and with inventors racing to develop the helmet of the future, the game will continue to change. It already has.

The NFL has been stricter in enforcing its rules to eliminate helmet-to-helmet contact, throwing down more yellow flags and eye-popping fines against its violators. In 2010, Pittsburgh Steelers linebacker James Harrison was fined $125,000 for illegal hits. Defensive players say they have been handcuffed compared to the generations that came before.

But this is still a violent game.

There is one gear for Green Bay linebacker Clay Matthews - fifth. There is one punch for Matthews - knockout.

He plays fearlessly and ferociously. But away from the game, out of the linebacker armor - quietly, privately - even this third-generation NFL player worries what this game will eventually to do his physical, emotional and mental health.

"There's no doubt, we're all going to feel the ramifications of our profession later down the line," Matthews said. "The way I play the game, I know there's going to be some repercussions."

Defensive lineman Ryan Pickett didn't think he was at any risk for concussions because he wasn't a running back or linebacker. He never had one in college or his first 11 years in the NFL.

But last year he went down to make a tackle and caught a knee to his temple. It knocked him out for a short time. It was a concussion and, to his surprise, he didn't come back quickly.

"I was like, 'OK, I can get myself back,' like you do with injuries when you're a football player," Pickett said. "I tried to get back on the field but I could never pass the test. I couldn't focus."

He would go to the store with his wife, Jennifer, and struggle to make the most basic decisions.

"It frustrates you and it irritates you," Pickett said. "That's when I knew how serious it was. It kind of scared me."

For good reason.

Just before two-time Super Bowl champion safety Dave Duerson of the Chicago Bears committed suicide in February 2011, he wrote a note requesting that his brain be examined for football-related damage.

He had been acting out, was estranged from his wife and in his troubled final years felt something was changing within him, mentally. To make sure his brain could be examined, he aimed the fatal bullet at his chest.

Boston University's Center for the Study of Traumatic Encephalopathy has analyzed the brains of dozens of former athletes, including Duerson, and revealed they suffered from CTE, or chronic traumatic encephalopathy, a form of damage to the tissues of the brain. It is believed to explain Duerson's depression, mood swings and general loss of personal control.

Former San Diego Chargers linebacker Junior Seau committed suicide in May at age 43. After a 12-year Pro Bowl career, he retired in 2010 and struggled with post-football life. He also had a domestic disturbance and was in a serious car accident. He also died of a self-inflicted gunshot wound to the chest.

Linebacker Vic So'oto, who re-signed with the Packers on Monday, is a second cousin of Seau's and close to the family, especially Seau's siblings. When So'oto made the Packers' roster last season as an undrafted free agent, he got a congratulatory call from Seau.

When Seau killed himself, So'oto wondered what everybody else wondered: Did Seau's NFL playing career and repeated hits to the head have a connection to his mental health?

"Everyone who knew him knew he was a happy-go-lucky type of guy," So'oto said. "For something like that to happen, there's got to be something different. That's one of the first things that popped into everyone's head. A section of his brain has been sent for research and we'll see what comes of it."

So'oto's mother begs him "every day" to stop playing.

He was an excellent student, a geography major, and thinks he will go to law school when he's done playing.

"I've been married for four years, have kids," So'oto said. "I definitely have the long-term perspective. But I am willing to sacrifice for a secure future, financially. For me it's being able to provide for my family. And if it comes at the price of a concussion, so be it. If my wife, who is one of the strongest people I know, can give birth, then I can go run over somebody."

That's a young man's perspective. Here's another. Former Green Bay offensive lineman Greg Koch's troubles began in his 40s.

He threw himself out of bed or walked in his sleep. The nights were terrifying; Koch would act out his dreams, and if that meant football, he was kicking and punching, and he would unintentionally hit his wife.

"When you're 6-5, 290, you can hurt somebody," he said.

The doctors said he had idiopathic REM sleep disorder and it is controlled through medication for now.

"The problem is you have a 50 percent greater chance of developing Parkinson's. Or early Alzheimer's," Koch said. "You're always looking to see if you have a little tremor in your hand."

At age 54, Koch also had developed cataracts in both eyes.

"The doctor said there's no way, at your age, you should have cataracts," said Koch, now 57. "The only time we see that is with repetitive head trauma."

Sources said numerous former Packers have been approached to join the ranks of class-action lawsuits being filed against the NFL over past treatment of concussions; Dorsey Levens, Santana Dotson, LeRoy Butler and Mark Chmura are among those who agreed to take action.

The total number of players involved in the lawsuit is "in the thousands," said a players union employee.

One former Packer, who did not want to be identified, said concussions weren't identified well in the 1960s and 1970s. Concussed players were simply asked to describe plays on the sideline, something any veteran could do without really thinking.

"I never took two weeks off for a concussion; I took off one, two plays," he said . "When we played, there was no such thing as an injury timeout."

This player, now in his 70s, has lived with knee and back pain and issues for 40 years, but it's getting lost on a familiar highway or street that worries him.

"I know I'm losing it," he said.

He said he will donate his brain for research when he dies.

Koch, a lawyer, has not joined the ranks of those suing the NFL. Even though he said he pays for his medical expenses on his own, and even though his total career earnings were less than $2 million, he is not interested.

"If I felt the NFL knowingly withheld information from me, that I could seriously damage myself, by not keeping me out of games when they should have, I might have a problem with it," Koch said. "But at the same time, the NFL gave me an absolute wonderful life.

"I signed up for broken bones and torn ligaments. I've had 11 operations because of the NFL. I knew that was all part of it. So you assume some of the risk." Preventing concussions

The goal for the NFL and the players union has boiled down to three strategies: prevention, recognition and treatment of concussions.

The NFL isn't using this technology yet, but accelerometers - electronic sensing devices - placed in helmets can measure the force of hits to the head. Sensing devices in the chin strap can measure the force of a hit and light up to alert coaches or referees of a possible head injury.

But the NFL does have modified helmets - such as those worn by Rodgers - that are layered with extra padding and protection in an attempt to cut down the risk of concussions.

Still, there is no surefire way to prevent a concussion in a collision sport.

"It doesn't matter what's on your head," said Kevin Walter, who runs the concussion clinic at Children's Hospital of Wisconsin. "If I hit you the right way, it's going to knock your head and it's going to shift your brain.

"I applaud equipment manufacturers for trying to come up with something, but the fact of the matter is, with contact sports there is always going to be this risk."

Everyone seems to agree the best goal is to prevent, or minimize, the risk of concussions. The best way to do that is proper tackling technique - no spearing, no leading with the head, no head-to-head collisions.

"I always tell coaches that the best helmet is the one that's not covered with the opposing team's paint at the end of the game," Walter said.

But players say even the best technique doesn't take away a split-second change in the angle of a tackler, or a bam-bam collision when players converge on a loose fumble.

That's why the focus is on the helmet.

Many players feel that the equipment is better, and some of them feel safer because of it.

The Packers may wear any helmet that has been approved by the National Operating Committee on Standards for Athletic Equipment (NOCSAE). The NFL said it has provided, along with the union, information to players on the testing of approved helmets under various circumstances to help players make more informed choices.

The NFL's Head, Neck and Spine Committee is working in conjunction with several engineers and two laboratories in performing tests on accelerometers - the force plates and chin-strap monitors - to see if they have the reliability, sensitivity and specificity to use for on-field NFL impact testing.

"Depending upon the results of the testing and the recommendation of the committee, accelerometers may or may not be used in the future," an NFL spokesman said. "Helmet manufacturers continue to evolve their designs and we hope players will wear the newer helmets."

John Michels was inspired to go into a career in medicine after he blew out his knee and his career ended after three years.

The former Green Bay tackle is now a resident in radiology in Houston. He's also working with the National Center for Human Performance in Houston. The group is putting together a proposal for the NFL for a new helmet science it has developed with NASA. It is not an accelerometer, but the group is seeking a patent for its invention.

"It should minimize the concussive forces associated with head trauma and also have a system that will alert when there has been a significant force exerted on the helmet," Michels said.

That could pique the interest of the NFL, since it is being discovered that concussions occur not in anterior, posterior or side-to-side hits, but in hits that result in a twisting, rotational acceleration of the head.

Mayer said larger, padded helmets and accelerometers will help those blows. There is even technology being discussed where sensors within the helmet deploy "like mini air bags to keep the rotational acceleration from occurring. That's certainly the helmet of the future."

In 2008 there were 200 reported concussions. In 2011, there were 260.

Mayer believes there weren't actually more concussions, they were just better identified.

Since he set out to honor NFL players union director DeMaurice Smith's request to change the culture of concussions in 2009, all teams had to follow a set of guidelines. The first was "one and done" - if someone has a concussion, has a loss of consciousness, amnesia, abnormal neurological exam or persistent symptoms, he's out of the game.

He cannot come back unless his neurological exam and neuropsychological testing demonstrated a return to his baseline testing, which was taken before he even set foot on the field. New this season, the Packers team physician as well as an independent neurological consultant - a neurologist, neurosurgeon or emergency physician who is not hired by the team - must both clear the recovering player.

The NFL also made the NFLPA's MACE testing mandatory on the sideline: a seven-minute test, adopted by the Department of Defense's Military Acute Concussion Evaluation, to detect whether a player suffered a concussion.

Hard-hitting Pittsburgh defensive back Troy Polamalu admitted he never reported some of his concussion-like symptoms so he could keep playing. Denver quarterback Peyton Manning said he sandbagged the baseline test once to make the results very low, and therefore very easy, in theory, to achieve even while still recovering from a concussion.

In other words, how long will it take for the culture to change?

Former Green Bay linebacker Jim Flanigan, who has a Super Bowl ring from the 1967 season, said he suffered several concussions. How did he know?

"Usually if you're lying on the ground for any length of time," said Flanigan. "Or, if you get hit on the right side of the head, it affects your left eye. So your eyes are crossed. But, if you had a 'dinger,' they'd give smelling salt - which is the worst thing, I guess, to do - to get you back to reality."

Flanigan, now 67, is in great shape, down to his high school playing weight of 225 pounds, still working out five to six days a week.

But he's battled dizziness, a tingly feeling in the fingers, balance issues and severe vertigo. He once had to be taken off an airplane because he was vomiting, his blood pressure was down and it was thought he was having a heart attack. Turned out that his heart was fine, it was the vertigo.

"I'm sure it's related" to his football days, he said.

He talks to the guys joining the class-action lawsuits. He knows players will be donating their brains for research. He will not.

"With a name like Flanigan, good Irish Catholic, what the good God gave me, I'm taking back with me," he said. "I'm not leaving anything here for someone to be probing about."

And yet despite their injuries, their long-term suffering, former players would not trade those Lombardi years for anything.

"If they invited me to come back, for the same lousy salary I got back then, only $15,000 a year, I'd do it," said the player who suffered too many concussions to count. "I loved it that much."

"They did a survey," Flanigan said. "They asked, knowing what you know now, the injuries, what you suffer through now, would you have pursued professional football? And I think the response was 87 or 90 percent yes."

By the time the Packers were pursuing their Super Bowl ring in the 1996 season, things had improved dramatically. One player from that era, who requested anonymity, said when he suffered repeated concussions, "our medical staff was very thorough. If you didn't pass the test, you couldn't go back in to the game."

Neuropathologist Ann McKee is one of the researchers studying chronic traumatic encephalopathy.

In an interview with sports website Grantland.com, she said she has found CTE, the neurodegenerative brain disease, in more than 70 athletes, nearly 80 percent of those she has examined. Now working in the Brain Bank at the Bedford Veterans Administration Medical Center in Bedford, Mass., she spends every Sunday rooting for her favorite team - the Green Bay Packers.

She hopes her favorite quarterbacks, Brett Favre and Rodgers, do not one day end up on her dissection table. That is the only way CTE is identified right now, in an autopsy.

"If you're worried about concussions, then you shouldn't be playing," said one veteran who requested anonymity who had one a few years ago.

The Packers declined to allow their trainers and medical staff to comment on this story, and through a team spokesman, Rodgers also declined an interview request. But some current players wonder if the risk of concussions is worth it to play the game.

"I don't want to end up mushbrain when I'm done with this game," guard Josh Sitton said. "I don't want to play for 15 years. I want to be able to walk when I'm 45. This game is not that important to me; my life after football is way more important to me."

One Packers veteran who played within the last five years - and who did not want to be identified - said even with proper technique, he suffered and played through concussions. The protocol, even just a few years ago, was to report the symptoms but keep right on playing if possible. "Yeah, that's the culture," he said. "I'll give the NFL credit. Over the last two years, they've done a much better job taking this on, of protecting guys from themselves. But the culture is always going to be: You need to be out there, trying to help your team win. I don't see that changing."

Now that he's retired, he worries what damage the concussions have done to his brain. It's almost a sick waiting game to see if he'll deteriorate.

"When you sign up to play, everyone knows there's some risk," said the player . "I expected some knee and shoulder issues. Guys talk about it all the time . . . 'Well, you signed up for this.' But I don't think guys sign up for traumatic brain injuries, Parkinson's and ALS and all these other things that have been linked to repeated head blows.

"Anybody who tells you they're not at least a little concerned is lying to you."