A couple of years ago, in the middle of the night, I crept downstairs to find my father sitting at the kitchen table, sobbing like a child.

My mother was beside him, trying to comfort him, an activity that took up more and more of her time. He was 87 and had dementia. It wasn’t unusual to find him upset or confused. But on this night, something seemed to be happening to him in real time — in 1941.

He was 6 years old, and was leaving Pittsburgh, the only home he had ever known, for an Air Force base in San Antonio, where his father had been ordered for duty. He and his parents were traveling there by train, transferring in Chicago.

It was the beginning of a lonely, difficult time for my father’s family, moving between Air Force bases in the South, where landlords sometimes turned them away because they were Catholic. An only child, he had been allowed to take one pet with him, a canary he was carrying in a birdcage.

As they were changing trains in Chicago, the bottom fell out of the cage. The canary flew out, up into the vaulted atrium of the station’s Great Hall. There was no way to get the bird — there was no time, they had to board a train to Texas. So my 6-year-old father shuffled after his parents, holding an empty cage.

In the years that had elapsed, he had negotiated arms treaties with the Soviets, had advised presidents, had served as a U.S. ambassador, all with the same watchful, wisecracking reserve. I thought I knew who he was. I could count on one hand the times I had seen him cry. Now here he was, sobbing over the canary as if it were yesterday.

This was all, it seemed, because of his brain. He had fallen hard in their house in Washington, D.C., smacking his head on the hardwood floor. Blood rushed into spaces in his brain, and cells starved of oxygen began to die. Eventually, he was diagnosed with vascular dementia, which is most often caused by strokes.

For five years after that, my parents lived with my family outside Boston, and we learned firsthand how brain injury affects behavior. My father recovered in some ways, but he became chaotic, his thoughts broken into mirror shards.

The biggest problem was that he had no idea where he was. Specifically, he did not know why he was living with us in Massachusetts, and no matter how many times we tried to remind him, over and over, he tried to leave. We would catch him packing the car, and gently — or not so gently — guide him back into the house.

This child-father was full of surprises. He bought surprising things: Five laptops! A cruise on the Norwegian fjords! Recurring $2 donations to every Democrat running for any office, anywhere! Once, in a weeklong cascade of Amazon deliveries, we received seven identical birdbaths from China.

With each step you take, coordinated contractions in your abdominal muscles help keep you stable and upright.

Now, new research finds that those gentle changes in tension and pressure also affect your brain, and may play a role in the organ’s overall health.

Imaging in humans and other animal species has long shown that the brain gently moves inside the fluid-filled skull cavity, but it’s never been clear what, exactly, is propelling this motion, said neuroscientist Patrick Drew, a Penn State University professor and associate director of the Huck Institutes of the Life Sciences.

Using advanced imaging, Drew’s team observed mice brains before and after the animals began walking. They realized that the brain actually moved just milliseconds before a mouse took a step — the brief moment when the animal’s abdominal muscles contracted in preparation for movement.

To test the observation, they strapped pressure sensors around the bellies of lightly anesthetized mice and observed the brain when slight pressure was applied only to the abdominal muscles. The same motion followed. Breathing or cardiac activity didn’t trigger the same response.

The connection, Drew and his colleagues determined, is the vertebral venous plexus, a network of veins that connects the abdomen to the spine in mice and humans alike.

“It’s like a hydraulic system. It really is very much like the jacks that push your car up, or something that an excavator might have,” Drew said. “Whenever you tense those muscles, which you do whenever you make a movement … that pushes blood into the spinal cord, it increases the pressure on your brain, and it moves your brain forward.”

The paper, which was published April 27 in Nature Neuroscience, answers a puzzling question about the mechanism controlling this long-observed cerebral movement.

It also puts forward hypotheses about why this belly-brain choreography exists.

Drew and his team ran computer simulations of fluid’s motion in and around mouse brains. The kind of contraction generated by walking moves cerebrospinal fluid out of the brain, leading Drew to hypothesize that the mechanism plays an important role in flushing out protein waste and other unnecessary material.

“It’s more speculative, but using simulations, we can see that this sort of motion should drive fluid movement and could help clear waste in the brain,” Drew said.

In future research, Drew said, the team would like to explore whether the brain is detecting these mechanical signals, and how physical conditions like obesity affect the hydraulic relationship between the abdominal muscles and the brain.

These current findings clarify the relationship between the brain and physical movement, illuminating fundamental mechanics that can apply to other research, said Michael Goard, an associate professor at UC Santa Barbara who studies sensory and spatial processing.

“He did, what I think is a very thorough job figuring out what’s causing this movement in the case of locomotion and tying down the mechanical elements,” Goard said.

The assessment covers seven simple movements — various lunges, jumps and timed balances — and produces a player score relative to the rest of the league and the player’s own history. The report also includes “jump” and “landing strategy” metrics that chart the distribution of force across a player’s hips, knees and ankles, and it translates arcana like “max ankle dorsification angle” into the lingua franca of basketball: “how small your ankle angle can get like when you get low on a quick first step.” The file, which a player can access throughout his career, regardless of team, is meant to give him information about how hard he can push his body — and, just as critically, when it’s time to ease off.

“When you’re younger, there’s days you can take as many — for us — baseball swings as you want,” New York Yankees first baseman Paul Goldschmidt, who is 38, told me. We were talking in mid-February at the team’s spring training facility in Tampa, Fla., as he was getting ready for eight straight months of baseball. “As you get older, there’s times when rest is more important than work.”

For some athletes, the right biometric data presented in the right context represents “permission to rest,” says Ana Montero, a co-founder of Atlas, a San Francisco-based company that makes brain-wave-scanning, behind-the-ear wearables about the size of Mentos candies. “It’s quantifiable evidence that is showing you: Dude, today — or right now — is not the day. Go to the gym, go for a walk, go for whatever it is. And then coming back and actually seeing that you’ve bounced back.”

The Atlas device gathers several types of data, including electroencephalography, or EEG, which measures electrical activity in the brain, and galvanic skin response, or G.S.R., which is what a polygraph test measures. That data is sorted into five categories (among them agility, vitality and stress) and then delivered with advice through a smartphone app.

“There’s always some noise in brain activity because neurons are not perfect chips or transistors,” André Marques-Smith, Atlas’s other co-founder, says. “So mistakes get made.” He adds that what causes neurons to lose their precision are things that we’re all familiar with: fatigue, stress, anxiety, hunger, aging. Tom Ryan, the N.B.A.’s senior vice president of basketball strategy, says Launchpad chose Atlas because it was eager to find a device that collected this sort of data in real time. If it works the way it’s supposed to, then a vet like Goldschmidt will know exactly when he’s good for some extra batting practice and when he should take a nap instead.