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 in the US.
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 excess proteins 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 the University of California, 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.
