Hours after suffering the worst injury of his life, Corey Hill had already forgotten it – at least temporarily. He woke up in a hospital bed and had no idea how he’d gotten there. He had a vague recollection that something terrible had happened to him, something too awful to be anything but a bad dream. It sat like a blurry image at the edges of his vision, and it disappeared when he tried to look right at it.

What was wrong with him? Why was he in the hospital? Some time in the night – or was it day? – a nurse came in.

“I’m looking at her like, ‘What the hell am I doing here?’” Hill recalled. “And she’s looking at me like, ‘You don’t know what happened, do you?’”

What happened was that Hill had suffered one of the most horrific injuries ever witnessed in a UFC fight. In a bout against fellow lightweight Dale Hartt at the UFC’s inaugural “Fight for the Troops” event in Fayetteville, N.C., in 2008, Hill aimed a kick at Hartt’s leg, just as he’d done countless times in sparring. Only this time Hartt brought his leg up to block the kick, so that Hill’s shin collided with his, bone on bone, in exactly the wrong spot.

Hill heard it before he felt it: that sickening smack, the sound of his right tibia and fibula cracking in half. In his memory, that sound is followed by his own muffled voice, screaming through his mouthpiece, “My leg! My leg!”

But then, once he stops and thinks about it, he can’t be sure if he really said that or just thought it. It’s one of many tricks of memory that the traumatic event played on him, not unlike what happened when he woke up in the hospital with the entire gruesome episode momentarily walled off in some inaccessible corner of his mind. That wall soon came down, though. Then the events of that night began to coalesce into one awful narrative, something that later sunk its roots deep into his memory, leaving Hill with the same question people with traumatic memories are sometimes never able to answer: Now what?

Maybe it’s a question that just refuses to stay answered. Surely, Hill has plenty of reminders. On a cold day, Hill said, he’ll feel it in the titanium rod inside his leg. He’ll stumble while walking – lingering nerve damage resulting from the injury has left him unable to fully extend the toes of his right foot – and suddenly he’ll be right back in that moment, the memory springing to life as if it’s happening all over again.

Smack. My leg! My leg!

And in his mind, the recovery process starts all over again.

* * * *

* * * *

Dr. Daniela Schiller has spent years researching how memories, especially traumatic memories, such as Hill’s, function in the brain. Those memories start out like any other, but because of the emotional content that comes with them, Schiller said, traumatic memories “are not normal memories.”

“Instead of being adaptive and helping you to function, they are very much disturbing,” Schiller said. “People just can’t function. They get depressed, they avoid places, and they suffer again and again from image retrieval. That’s not the way memory is supposed to function.”

That’s partly because, when it comes to how memory is supposed to and does function, Schiller maintains that a lot of our usual assumptions are flatly wrong. Too often, Schiller said, we think of our memories as fixed recordings of the past, filed away in our brains and just waiting for us to pull them up on the big screen, like surveillance camera footage of the past. But our memories don’t truly function that way, and were probably never intended to, according to Schiller.

“The function of memory is to help you understand the present and maybe make some limited predictions for the future,” Schiller said. “It’s not really about recording exact events from the past.”

Partial proof for that hypothesis lies in how malleable our memories are. Not only are they not always reliable while we’re recording and storing events, they also don’t stay the same once we put them away in the brain’s memory bank. They are constantly being updated, revised and recategorized. We are altering our own memories all the time, never more so than in the instant that we recall them.

“What’s happened in the last decade, initially in studies in animals, is that there is a stage where the memory becomes vulnerable again, just as it was in the beginning when the memory was formed, before it was stored and consolidated,” Schiller said. “This happens almost every time we retrieve a memory. The act of retrieval, the act of remembering, it makes the memory active in the brain, and then it has to be stored again.”

It seems intuitive, once you stop to think about it, but it’s not something we tend to acknowledge. It’s also something that’s only recently been documented in a laboratory setting.

Picture your memories as books on a shelf in a vast, meandering library. When you take a memory off the shelf and open it up, you aren’t entirely in control of what happens next. The memory may be from the past, but the emotions it evokes, whether positive or negative, take place in the present.

“That’s the best evidence of a memory, what you feel now,” Schiller said. “It’s just the interpretation of it and the actual details and the explanation of an emotion. Then it becomes inaccurate or inconclusive.”

As you’re standing there reading this particular book from the memory library, you don’t necessarily experience it in exactly the same way each time. You are, in a sense, rewriting the book as you are reading it, depending on the context in which you take it off the shelf, and what you tell yourself about it once you’ve got it in your hands.

When you’re done, you put the memory back on the shelf, but the book is different now. It doesn’t always get put back on the same shelf, or even the same section. So could a memory that was once classified under “Terrible Things That Have Happened to Me” be moved to a different section? Could you rewrite that book enough that a horror story becomes an inspiring adventure tale?

According to Schiller, we can and do. We do it all the time, in fact. And once you talk to Hill about his experience dealing with a traumatic injury, you realize that he has done this very thing, slowly, over the course of several years, and without ever knowing that he was doing it.

* * * *

It took him two years to watch the video. Hill knew it was out there, waiting on some darkened stretch of the information superhighway, just waiting for him to do a Google search of his own name and go careening into the nightmares of his past. He avoided it as long as he could. Maybe, he thought, he could avoid it forever. Maybe he’d never have to see what others saw, to get that outsider’s perspective on his own mini-tragedy.

“I think that was a big mistake,” Hill said. “I was trying to forget about it without reliving it, but reliving it is exactly what I had to do.”

Hill’s life had changed dramatically by the time he sat down and forced himself to watch the fight – all of it, in slow-motion. He was no longer a UFC fighter, no longer thinking of himself as the phenom with the brightest possible future. He’d been released from his contract after the injury, since no one could even be sure if he’d ever fight again. He’d returned to fighting in January of 2010, just a little over a year after breaking his leg in the cage, but he was still carrying around the emotional baggage from that night in North Carolina, not to mention the physical scars.

Hill suffers from a condition known as drop toe, due to the neurological damage of the leg break. Being unable to extend the toes of his right foot, Hill said, makes it feel like “I’ve pretty much got a fist of toes in my shoe, 24-seven.”

When he returned to training, he found that he couldn’t do all the things he used to. He couldn’t push off or rotate properly on his punches, and he’d more or less resigned himself to taking kicks completely out of his arsenal, he said, “because what if it happened to me again? Then I’d be that idiot who went out and did the same thing that got him hurt.”

“Some of those times were dark in the gym, and it was hard to not blame it on the injury,” Hill said. “It’s rough to continue on. I had my family looking at me like, ‘Hey, you can do other things.’ But I wasn’t ready to let it go that easily.”

That’s the part that a lot of people don’t understand, especially these days, Hill said. Now he’s 36, riding a four-fight losing streak and competing sporadically, usually on short notice, and almost always against opponents who are either on their way up and looking for a name to beat on the small circuit, or else, Hill said, “they just need the money.”

But Hill could do other things. He’s finishing up a degree in education at Pasco-Hernando State College. He has a wife and three kids, and continuing to fight at this point is, he acknowledges, “a little bit selfish.” So why do it?

Part of it was a refusal to accept what the injury had done to him. He didn’t want to let it end that way, he said. But another part, whether or not he realized it at the time, was an attempt to rewrite his own memory of that traumatic event.

It makes a certain amount of sense, when you think about it. If Hill had called it quits after the injury, he’d always look back at that broken leg as the thing that ruined a promising MMA career. That memory would stay locked in a dark room of his mind, a room where he catalogued the awful times in his life when important things were taken from him. Every time the memory resurfaced – as it was bound to do not only when he felt the physical effects on a cold day, but also when someone like former UFC middleweight champ Anderson Silva suffered an almost identical injury in December 2013 – he’d be flooded with negative emotions. The memory would retain a unique power to torture him indefinitely.

Instead, Hill made it mean something different. He turned the injury into an obstacle he overcame. He used it as proof of his mental fortitude, his toughness, and his resolve, since who but a major tough guy would keep fighting after something like that?

“It wasn’t until I got to that point that I started to realize, this injury isn’t the last of me,” Hill said. “This, like 90 percent of what happens to you in life, is what you make of it. You have to keep living.”

This also explains Hill’s response to another aspect of Schiller’s research. Although it’s far from a reality at this point, Schiller believes that we might eventually have the power to target certain memories and effectively block them from popping up again. It’s already been done in studies with mice at the Massachusetts Institute of Technology, where neurologists used a technique known as optogenetics to effectively switch certain negative memories off.

We’re still a long way from being able to do the same in humans, Schiller cautioned, but it may very well be an inevitable development at some point in the future.

“If there’s a stage where the memory is prone to interference, you could potentially block it with drugs, or you could use some kind of behavioral intervention, like sort of exposure therapy, but timed to the stage where the memory is most vulnerable or prone to interference,” Schiller said. “Memories naturally get updated. If you could time it to that stage, you could capitalize on that.”

Think “Eternal Sunshine of the Spotless Mind,” which also happens to be the movie that motivated Schiller to dig deeper into memory research. As a second-generation Israeli, she said, she grew up fascinated by how some people in her parents’ generation managed to deal effectively with traumatic memories of the Holocaust, while others never got over them. At least, that’s the answer she gives when you ask why she got into this field to begin with. Then again, her research has made her skeptical about such neat explanations.

“Sometimes you do things just because you do them,” Schiller said, “and you only assign a reason later on.”

That very human impulse is also a part of what makes our memories such difficult hurdles to get over, Schiller said. People tend to dwell on their past, to look for reasons even where none exist. It’s why you’ll hear people say that “everything happens for a reason,” often while sounding like they’re trying to convince themselves first and foremost.

Schiller doesn’t necessarily buy this, she said. It’s very possible that the universe is a place of random, meaningless collisions, and our attempts to delve into our own past in search of reasons or explanations “might be useless,” she said.

Still, it’s a tough impulse to resist. Hill couldn’t help but search for meaning in his own misfortune. He found some too, which is why he doesn’t have to think too hard about whether he’d want such a scientific intervention for his traumatic memories, even if it were free and easy and immediately available.

“That memory is absolutely vital for me,” Hill said. “Each time things get hard, and each time I question whether I can do this, I retrieve that memory of the injury, and I think, ‘You’re the guy who broke his leg in front of the whole world, and you had the heart to continue.’ That memory keeps me strong. It reminds me of who I am. I really feel like if I didn’t have that memory, I don’t think I’d be as strong a person as I am right now.”

It’s a question that goes to the core of what it means to be a person. Who are you, if not a collection of memories and responses, emotions and impulses? What do any of your experiences mean, if not exactly what you’ve decided they do? Take one of them away, and what are you left with? Who are you? How do you know?