We already know that moving your body is important for brain health, but a new study reveals a possible reason why: It could be triggering a kind of hydraulic pump that flushes out fluid in the brain. By studying mice and conducting simulations, researchers at Pennsylvania State University have found that movements in the abdominal muscles can ripple up to the brain, potentially cleaning out waste materials that build up during the day.
"Our research explains how just moving around might serve as an important physiological mechanism promoting brain health," says Penn State neuroscientist Patrick Drew. "In this study, we found that when the abdominal muscles contract, they push blood from the abdomen into the spinal cord, just like in a hydraulic system, applying pressure to the brain and making it move."
Since mice are mammals, their bodies work similarly to ours. In this study, the researchers peered through windows in the skulls of living mice, using two-photon microscopy to capture high-definition images. When the mice walked on treadmills, the scientists could see their brains shift immediately after the abdominal contraction that comes right before the mouse takes a step. By applying light pressure to the abdomens of anesthetized mice, the researchers confirmed that this was the source of the brain's shift.
"Importantly, the brain began moving back to its baseline position immediately upon relief of the abdominal pressure," Drew says. "This suggests that abdominal pressure can rapidly and significantly alter the position of the brain within the skull." Perhaps our brains are getting the same treatment when we step up from a lunge or twist in a yoga pose.
Micro-computed tomography (CT) scans revealed the network of veins that make up this 'pump' between the abdominal cavity, the spinal cord, and the brain. To account for the complex physics involved, researchers used computer modeling. "The brain has a structure similar to a sponge, in the sense that you have a soft skeleton and fluid can move through it," explains biomedical engineer Francesco Costanzo. "Keeping with the idea of the brain as a sponge, we also thought of it as a dirty sponge – how do you clean a dirty sponge? You run it under a tap and squeeze it out."
Their simulations revealed that the subtle movements in the brain, triggered by abdominal tensing, would be enough to push cerebrospinal fluid (CSF) into the subarachnoid space. Research has shown that CSF flow is important for removing waste products that can otherwise contribute to neurodegeneration.
Interestingly, in sleep, CSF flows in the opposite direction, soaking into the brain from the subarachnoid space. This research offers a possible explanation for why flow varies so drastically between sleep and waking. "This kind of motion is so small. It's what's generated when you walk or just contract your abdominal muscles. It could make such a difference for your brain health," says Drew.