Former National Hockey League star Jeremy Roenick says that at age 19, he was knocked out of a game with a concussion that caused him to lose consciousness for 15 minutes.

Though he has no recollection of how he got from the ice to the Chicago Blackhawks locker room, the sole treatment he received that day was being given an ice pack to put on his head. He says he was back in the lineup the very next evening.

During the rest of his 20-year career with the Blackhawks, Phoenix Coyotes, Philadelphia Flyers, Los Angeles Kings, and San Jose Sharks, Roenick, now 44, would suffer at least 12 more concussions — an injury defined by the Centers for Disease Control and Prevention as when a person takes a blow to the head that changes how that person's brain functions.

The repeated blows to the head found in contact sports have also been linked to chronic traumatic encephalopathy, a degenerative brain disease that has been found in several high-profile athletes who have committed suicide.

Like most of his peers who played during the 1980s and 1990s, Roenick was unaware of the long-term effects concussions can have on athletes who suffer from them, a group of symptoms that can include memory loss and depression.

And, like many who competed in professional football, hockey, and other sports during that era, Roenick is dealing with the consequences of his injuries long after he stopped playing.

Five years into his retirement, the nine-time NHL All-Star says that the brain damage inflicted by his hard-hitting career makes it so he can no longer remember many parts of his past — games he played in, trips he went on, and friends he spent time with.

"My wife will ask me, 'Hey, remember we did this? Remember we did that?' And I totally don't remember any of it," Roenick says. "My short-term memory is good, but there's a lot of times I'm asked questions that I couldn't remember for the life of me."

Now an analyst with NBC Sports, Roenick says the concussions also hinder his speech. Sometimes on television he will have trouble finding the right word, even if it's one he knows and uses frequently.

He's worried that his brain will continue to deteriorate as he gets older, and he fears that he could one day suffer from dementia.

"It's extremely frustrating, and I get mad because public speaking is part of my job," he says. "There are a lot of things that I know, but I can’t go in my brain and retrieve the word that I’m looking for and throw it out of my mouth."

Roenick, right, at a Players Against Concussions event in October. Eugene Gologursky/Getty Images To prevent future generations from being left with the same feelings of anger and frustration, Roenick teamed up with former Chicago Bears football star Jim McMahon earlier this year to form a nonprofit group called Players Against Concussions.

The group seeks to educate young players and their parents about what happens to their brains after they are concussed and to facilitate more research on the topic.

Still, there is only so much education can do. Roenick says that had he known during his playing days what he knows now, he would have taken more time off to heal from injuries — but he would not have changed his self-described "reckless" style of play.

While he applauds the efforts the NHL has taken to limit the damage concussions do to its players, he says that as long as people are colliding while skating at 30 mph, head injuries are always going to be part of the game.

For its part, the NHL has instituted rules mandating that players be taken out of games if they appear to have concussions and requiring them to be taken immediately to a quiet room for examination by a doctor. It has also barred hits that target a player's head.

"There’s no way to avoid it, but the NHL has done a really good job of making sure the players that get it are immediately put into a quiet room and put out of action until they can pass certain tests to make sure the brain has enough time — about a week — to heal," Roenick says. "And that's as good as you can possibly get."

Not everyone agrees with Roenick's assessment of the league's actions.

Since November 2013, more than 200 former players have filed a series of lawsuits against the NHL alleging that the league hid concussion risks and failed to take action to protect its players. The lawsuits were consolidated into a single case this August, and the legal dispute remains ongoing.

Another skeptic is Dr. Michael Cusimano of Toronto, who published research last year finding that the rules barring hits targeting the head had done nothing to reduce the rate at which players suffered concussions. According to his study, there are about five concussions for every 100 NHL games.

Dr. Cusimano says that if the league were really serious about curbing concussions, it would ban fighting and issue harsher penalties for players who give illegal hits to opponents' heads.

"It should be of concern to all of us because our brains are our most important aspect of ourselves — they really define us," Cusimano tells Business Insider. "So whenever anyone gets a brain injury, it should concern people."