Penn State Study: Abdominal Muscle Contractions Drive Brain-Cleansing Fluid Flow in Mice

Exercise benefits the brain through a mechanical process that acts like a rinse, according to a new study from Penn State researchers published in Nature Neuroscience.

The study points to abdominal muscles as the key. In mice, the brain connects to the abdomen via blood vessels that work like a hydraulic system.

"Every time the mice contract their abdominal muscles — like when they walk — blood moves from the abdomen into the spinal canal," said lead author Patrick Drew, a professor of engineering science and mechanics, neurosurgery, biology and biomedical engineering at Penn State, in a press release.

That blood movement creates slight pressure on the brain. The brain then shifts or sways a bit inside the skull.

The brain floats in cerebrospinal fluid, a clear liquid that clears out cellular waste. Waste buildup has ties to neurodegenerative diseases such as Alzheimer’s, Drew noted.

Advanced computer simulations showed that brain motion drives cerebrospinal fluid through brain tissues. That flow could carry away waste products.

"Our research explains how just moving around might serve as an important physiological mechanism promoting brain health," Drew said.

To test abdominal pressure as the main driver, researchers pressed gently on mice bellies. The pressure was less than in a standard human blood pressure test. Even without exercise, it shifted the brain and started fluid flow.

"We were surprised at how tightly linked the brain motion was to the abdominal muscle contraction," Drew said.

The team noted limits. The work used mice, not humans, so more studies are needed to check effects in people. Simulations tracked fluid movement instead of direct measures in living brains.

"Our research shows that a little bit of motion is good, and it could be another reason why exercise is good for our brain health," Drew added.