A prominent neurosurgeon watched speed skaters slowing down at the crucial last stretch of a race during the Winter Games, and listened to analysts explaining the painful buildup of lactic acid in the Olympians’ thighs. And he thought: “They’re very focused on the muscle part of athletics.”

In the future, he figured, they will be much more interested in the brain.

What do neurologists and others who study the brain see when they watch the world’s best athletes compete in this Winter Olympics? Many see brains propelling people to extraordinary things, allowing them to spin and flip without dizziness, to adapt quickly, to anticipate challenges — or, sometimes, to choke.

“I like watching really talented, amazing athletes,” said Kathleen Cullen, a professor of biomedical engineering and co-director of the Johns Hopkins Center for Hearing and Balance. “It’s beautiful to see what the body can accomplish . . . particularly beautiful because I’m thinking about the computations required to do it.”

A snowboarder flying through a double McTwist, or a skater spinning out a triple Lutz or an Axel, she explained, possesses a brain that has built models for those intricate maneuvers. “What makes Olympic athletes unique is the ability to create really complex models of self-motion and movement they expect as they complete these very sophisticated routines,” she said.

Not just that: They can recalibrate on the fly. Their ability to adapt to the unexpected during the routine is not something the average person can do, she said.

Cullen studies the neural mechanisms that encode motion. She looks at the ways the brain uses information from the vestibular system in the inner ear — the “sixth sense” that gives people a sense of where they are, how they are moving through space — and other sensory mechanisms to help navigate the world.

“The sense of vision is very slow,” she said. “If you’re slipping on ice and waited for the visual system to tell you you’re slipping, it would be game over.” But if the incoming sensory information from the inner ear is different than what the brain expects (as when falling suddenly on ice), that can be sensed within milliseconds, she said.

Kathleen Cullen. a professor of biomedical engineering at Johns Hopkins University explains how skaters and skiers adapt to handle the disorientation. (Johns Hopkins University)

This helps snowboarders, for example, when they’re flying through the air; the brain receives moment-to-moment updates about where the head is and from the muscles about where arms and legs are relative to the rest of the body, all of it arriving within milliseconds. The brain then compares the information it has learned to expect with the snowboarder’s actual motion, so that it can send an appropriate signal to the spinal cord to rapidly adjust balance within milliseconds.

Most people feel dizzy after they spin because fluid in the inner ear continues to move, giving the sensation of continued motion. A figure skater who’s constantly twirling on the ice can teach herself to counter that natural sensation. She can train herself to use an object after spinning as an anchor to let herself know how she is moving.

But there’s something more profound that happens over years of repetition in practice: The brain learns to better interpret the information coming from the inner ear; it recognizes, in effect, that the sensation of spinning is false when the body has actually stopped spinning.

The athletes’ “ability to build and recalibrate these models is really impressive,” Cullen said.

For a figure skater who is pitching backward intentionally during his routine, the challenge is resisting the reflex that normally prevents a skater from falling over, said Nathaniel Sawtell, a neuroscientist at Columbia University’s Zuckerman Institute. Those reflexes are hard-wired in the spinal cord and the brain stem, he said, and trying to override them doesn’t happen perfectly at first. But over time, with repetition, skaters are able to do it.

Motor skills might seem relatively basic, he said, “but these are amazing feats of learning that are really a great scientific puzzle, and a challenge to understand how we do these incredible things.”

Even the most amazing robot, he said, “is nothing compared to humans playing sports.”

Great athletes’ brains need to be able to predict what is going to happen, and adapt quickly, said Jam Ghajar, director of the Stanford Concussion and Brain Performance Center, where, among other things, they train athletes to improve performance. “With Olympic athletes, it’s incredibly important to get their timing,” and react to a bump in the snow or a patch of ice at high speed, Ghajar said.

That’s what really sets Olympic athletes apart, said Christopher Fetsch, an assistant professor of neuroscience at Johns Hopkins — not their bodies so much as their brains’ speed and flexibility in taking in sensory information and translating it into muscle movements.

Chris Fetsch, a neuroscience professor at Johns Hopkins University explains what sets apart an elite athlete is the quickness and flexibility of their minds. (Johns Hopkins University)

He watched, fascinated, as skiers pushed themselves right to the edge of falling — going as fast as possible without crossing the threshold of losing control. It’s somewhat related to the research he does at Hopkins’s Zanvyl Krieger Mind/Brain Institute. “In our day-to-day lives, we make countless small unconscious decisions like this. In the Olympics . . . the stakes are much higher, the world is watching, but the processing going on in the brain is very similar. In these athletes, it has been honed to perfection to perform a particular skill.”

No matter their physical ability, athletes need to be able to handle the intense pressure that comes with competition. And stress originates in the brain, where chemicals cause blood pressure to go up, and can trigger hyperventilation, said Judith Kupersmith, a professor of clinical psychiatry at Georgetown University School of Medicine. So Olympic athletes need to learn how to handle that increased heart rate and other reactions that make it difficult to focus and perform as usual.

“Some people are wired in such a way that they can deal with it more easily,” Kupersmith said. And some learn to control the emotions that come from those brain chemicals. She runs a clinic for people in the performing arts such as ballerinas and violinists to help them handle the pressure of performing.

But competing is different than performing, she noted: In the Olympics, the fate of an athlete often hinges on a single moment, a tiny amount of time, and that increases the pressure enormously.

With so much at stake, it’s easy to see why some athletes choke. Vikram Chib, assistant professor of biomedical engineering at Johns Hopkins, who studies how our brains process incentives and how that influences performance, sees potential parallels between the lab and the Olympics.

In his research, when people are paid to do certain tasks, performance increases along with the incentive — until the reward gets too big. Then, researchers see the opposite effect. When the subjects see a potential $100 reward, a scan shows “their brain lights up: ‘I have $100 to gain.’ ”

But when the subjects actually do the task, researchers see activity in another part of the brain. “The brain activity looks like they are thinking they have $100 to lose.” And performance deteriorates.

So when a gold medal is at stake, Chib said, athletes who can keep their minds off the possibility of losing are those more likely to perform well — and win.

There’s another thing that can help give athletes an edge, Ghajar said, that has nothing to do with training in the gym. It’s simple: rest. “A major part of brain performance is getting enough sleep.”

Vikram Chib, a biomedical engineering professor at Johns Hopkins says the brain activity of Olympic athletes can reveal who will choke under pressure. (Johns Hopkins University)