Research suggests that bowel movements may clear excess material from our brains

With each step you take, the combined contraction in your abdominal muscles helps you stay stable and upright.

Now, new research finds that those subtle changes in stress and anxiety also affect your brain, and may play a role in the overall health of the organ.

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

Using advanced imaging, Drew’s team visualized the mice’s brains before and after the animals started walking. They noticed that the brain actually moved just milliseconds before the mouse took a step – the short time when the animal’s abdominal muscles contract in preparation for movement.

To test that observation, they attached pressure sensors to the stomachs of lightly anesthetized mice and saw the brain when only mild pressure was applied to the stomach muscles. A similar move followed. Neither respiration nor cardiac activity elicited the same response.

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

“It’s like a hydraulic system. It’s a lot like the jacks that push your car up, or something that an excavator would have,” Drew said. “Whenever you tighten those muscles, what you’re doing whenever you’re making a movement … that’s pushing blood into the spinal cord, increasing the stress on your brain, and moving your brain forward.”

I paperpublished on April 27 in Nature Neuroscience, answers a puzzling question about the mechanism that controls these brain movements that have been studied for some time.

It also hypothesizes why this belly-brain choreography exists.

Drew and his team conducted computer simulations of fluid movement in and around the mouse brain. The type of contractions produced by walking drain cerebrospinal fluid from the brain, leading Drew to hypothesize that the mechanism plays an important role in removing protein waste and other unnecessary substances.

“It’s very speculative, but using simulations, we can see that this type of movement should drive fluid movement and may help remove waste from the brain,” Drew said.

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

The current findings clarify the relationship between the brain and body movement, which illuminates basic mechanisms that can be applied to other research, said Michael Goard, an associate professor at UC Santa Barbara who studies sensory and spatial processing.

“He’s done, I think, a very thorough job of finding out what’s causing this movement in terms of the displacement and binding of the equipment,” said Goard.