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.

The deadly fires that devastated homes in Pacific Palisades and Altadena also laid waste to a lush canopy of leaves and pine needles that had cooled and shaded residents here for generations.

Now, more than a year later, trees that had survived the flames are disappearing at a troubling rate.

Since the January 2025 fire siege, roughly 20% of surviving street trees have gone missing, according to preliminary results from a University of California research team.

Many of the hundreds of missing trees probably would have recovered from the damage they suffered in the fires, experts say.

The results from the survey of about 500 trees in the Palisades and 1,500 in Altadena — including conifers, palms, Chinese elms and carrotwoods — seem to confirm worrying patterns observed by arborists and local volunteers in the burn scars, who said losses will probably continue for years to come.

Several factors appear to be at work.

Even as the Palisades and Altadena rebuild, local governments only undertook limited efforts to water recovering trees. At the same time, building contractors have been quick to remove trees that stand in the way of construction, while debris removal crews have cut down living trees that they mistakenly identified as dead.

In response to the continuing loss of trees, a group of arborists and volunteers are working to keep the recovering trees alive — and hopefully someday start planting the next generation of the burn scars’ urban forests.

While many homeowners view trees through the lens of maintenance costs — regular pruning can be expensive, and tree roots can wreak havoc on sidewalks and underground pipes — the benefits of trees are numerous and well-documented, experts say.

The shade they provide and the process of evapotranspiration — where water on the surface of leaves evaporates and carries away heat similar to how human sweat works — can cool neighborhoods by more than 10 degrees. This cooling reduces the risk of heat illnesses and can lower homeowner energy costs.

Trees also improve air quality, improve residents’ mental health, and reduce the risks of flooding and landslides. Meanwhile, fire experts say that reasonably spread-out and well-maintained trees do not pose a significant fire risk.

Edith de Guzman, a climate change, water and urban forestry researcher with UCLA, has been studying the burn area trees with her team. The researchers did their first assessment in the months following the fire, and donned orange vests to do it again this past month.

Edith de Guzman uses a hypsometer to calculate the height of a tree in Pacific Palisades.

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Their discovery that roughly two out of every 10 trees the team went back to check on were missing was particularly concerning to De Guzman because her team was only looking at public street trees — which the city and county have authority over and work to protect — as opposed to trees on private property, which are maintained or felled largely at the discretion of the property owners.

“On private property it’s a different story — except for protected species,” she said. Public trees, however, “we are still seeing removals that are unnecessary, and the city is not sure who is responsible.”

L.A. City Bureau of Street Services did not respond to a request for comment.

The fires themselves killed and damaged a significant fraction of the areas’ urban tree cover — both private and public — although precise estimates are hard to come by.

Almost immediately, the surviving trees faced trouble.

David Card, board president of the Palisades Forestry Committee, said shortly after the fire, trees began to fall. In the chaos of the aftermath, it was unclear what organizations — or what agencies — were responsible.

Rebecca Latta, co-founder of Altadena Green, said that when the U.S. Army Corps of Engineers debris removal efforts began, leadership worked with them to save trees but that the Army Corps’ contractors often pressured homeowners to approve tree removals and incorrectly identified native oak trees — which did not have leaves at the time — as dead.

Chinese elm trees rise over Pacific Palisades.

Once private contractors arrived to begin rebuilding, they often removed trees on private properties they determined were in the way — and sometimes even removed public street trees they did not have authority over, the advocates said.

At the same time, neither the city of Los Angeles nor the county have routinely watered surviving public trees — which arborists say is essential to helping damaged trees recover. The county did one round of watering in Altadena, but found it to be too expensive, Latta said. The city conducted no watering in the Palisades due to a lack of resources, according to Card.

L.A. County Public Works said it remains “committed to preserving the community’s public trees.” It routinely waters newly planted trees and will continue to assess the needs of mature street trees, the department added.

So, local groups are stepping up to save the trees.

The Forestry Committee began sending two watering trucks around the Palisades: a 2,000-gallon tanker from a landscaping company and a 500-gallon tank on the back of a trailer. Altadena Green began conducting property tree surveys to help residents understand which damaged trees would probably survive and how to take care of them.

The Forestry Committee is also working on a long-term tree planting program for the Palisades that will utilize fire-resilient tree species — although the Los Angeles Department of Water and Power asked the Forestry Committee to hold off for a year as it starts working to move power lines underground, Card said. Excavation will probably occur on plots where street trees are typically placed.

Researchers Oliver Khachikian, Matthew Murphy, Mariana Vargas and Sophia Riemer prepare to survey trees near Aiglon Plaza in Pacific Palisades.

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In the meantime, saving existing trees remains the tree doctors’ priority.

Laura Travnitz, an Altadena resident who lost her home in the fire, recalled an Army Corps contractor pressuring her to remove more than a dozen fire-impacted trees on her lot. Now, they’re just stumps. Some already have little green shoots reaching up toward the sky.

“I’m 65,” she said. “I’m not going to be around for those to grow again.”