Over the years, UFC audiences have seen an arm get broken in four places, an ear half ripped off and teeth sent flying from the cage. Yet the ailments hanging over UFC, and all contact sports right now, are brain injuries. A recent study of deceased NFL players' brains showed that 110 of 111 of them had chronic traumatic encephalopathy (CTE), a degenerative brain disease associated with repeated trauma to the head. Meanwhile last year, Jordan Parsons was the first MMA fighter to be publicly diagnosed with CTE after he died at 25 in a traffic accident.

While many brain diseases don't become apparent until later life, CTE can only be identified posthumously. It's only now that a generation of MMA fighters are retired and discovering the long-term effect the sport has had on their brains.

"It's a relatively young sport," said Robert Cantu, the co-founder and medical director of the Concussion Legacy Foundation and a clinical professor of neurosurgery at Boston University School of Medicine. "The amount of research that's been done is trivial."

There are also many questions around CTE, such as whether there's a threshold of hits to the head one can take before the disease risk shoots up and what makes some people more susceptible to it than others.

"The body doesn't adapt to being punched in the head at all ... You don't get used to it."

The most comprehensive ongoing research is the Professional Fighters Brain Health Study at the Cleveland Clinic, partially funded by the UFC, which has been giving MRI scans and cognitive tests to current and former fighters once a year since 2011. Meanwhile, a University of Toronto study found that 32 percent of UFC fights between 2006 and 2012 resulted in head trauma -- a higher rate than ice hockey and football. Yet most injuries happen in training.

For the UFC, that means a change in mind-set: While blows to the head are inevitable in the ring, they can be minimized in sparring. "You shouldn't compete every day. You shouldn't put yourself in a win-or-lose situation where you're going to go 100 percent with another human being every day," said the UFC's Griffin. When he was competing, Griffin would spar two or three times a week for as many as 10 rounds, which he now calls "unnecessary." It's part of a mentality in some fighters that the more you spar and get hit, the more prepared you are for the fight. "The body doesn't adapt to being punched in the head at all," he said. "You don't get used to it. You don't build up calcium deposits."

An Octagon at the performance center equipped with 12 VICON cameras next to an 82-inch touch screen for video analysis is supposed to encourage athletes to fight less and analyze their spars more, something Griffin says he did at most five times in his career.

However, to some experts, brain injury is going to be inevitable for UFC athletes, and it's unclear how much tech-assisted training methods can stop that.

"That's part of the culture. If you can knock a guy out in MMA with a shot to the head you're going to do it," said Shelby Karpman, chief medical officer for the Edmonton Combative Sports Commission in Canada. Karpman has worked as a ringside physician in boxing and MMA fights since 1992, handling about a half dozen annually; this September he saw UFC fighter Gavin Tucker get four bones broken in his face in one fight.

"The fans love to see people get hit in the head," Cantu said. "So those fighters tend to learn to strike because they make more money and they are more popular. Long-term, later-life ramifications of all that head trauma is going to be a reality."

The knockouts, after all, are what everyone is here to see.