Later, in August 2010, posters were distributed in locker rooms to warn players that head injuries could have lifelong consequences.
The poster warned that a traumatic brain injury can cause a wide range of short or long term changes affecting thinking, sensation, language or emotions, according to the Centers for Disease Control and Prevention. It also warns that the changes may lead to problems with memory and communication, personality changes, as well as depression and the early onset of dementia.
Earlier, in March 2009, the league acknowledged that careers in the NFL could lead to neurological and mental health problems.
Dr. Wendy Wright, a neurologist at Emory University in Atlanta, said in 2009 that she was pleased to see that the policy that kept players from returning to a game or practice if they'd lost consciousness was more conservative than she expected.
She acknowledged that care needs to be taken when a player's career is at stake, "but when you're talking about protecting the brain from long-term consequences of injury, as a neurologist, of course, I think you can't be too careful."
The New York Times reported that Duerson was the first player to request that his brain be examined after his death for CTE, but that as an active member of the players union, he was likely all too aware of the disease. It's been reported that he believed he had the disease in the months before he died.
In the past, players had been cavalier about playing with an injury, even concussions. In an Associated Press survey of 160 active players in 2009, 30 said they had hidden or played down the effects of a concussion at some point in their careers.
But Dr. Kenneth Perrine, a neuropsychologist at Hackensack University Medical Center in Hackensack, N.J, said players had become more aware of the seriousness of concussions in recent years and more candid about feeling ill effects.
"They realize that this is their profession, this is their game, but it's also their lives, and they want to make sure that they're not going to do something that's going to have a negative impact down the line," he said.
Nowinski said that athletes need to know that they need to see a doctor to be cleared to play after a head injury.
"The brain is far more fragile than we've ever realized," said Nowinski. "When you get a concussion, know your brain needs time to recover before you make the injury far worse."