A surprising new effect of yawning on brain function has been uncovered by researchers at the University of New South Wales in Australia, who found that yawning influences the flow of cerebrospinal fluid in ways scientists did not expect.
For the study, researchers used MRI scans to monitor changes in the heads and necks of 22 healthy volunteers while they yawned, took deep breaths, suppressed yawns, or breathed normally.
Scientists initially expected yawning and deep breathing to produce similar results because the two actions share several mechanical features. However, the scans revealed a striking difference.
According to the findings, yawning appeared to push cerebrospinal fluid away from the brain – the opposite effect observed during deep breathing. Cerebrospinal fluid surrounds the brain and spinal cord, helping protect and nourish the central nervous system while also removing waste products.
Researchers noted that the effect did not appear in every participant and was observed less frequently in men. They added that technical limitations linked to MRI imaging may have influenced some of the measurements.
The study also found that both yawning and deep breathing increased the flow of blood leaving the brain, creating space for fresh blood to enter. Unlike cerebrospinal fluid, however, blood flow did not reverse direction during yawning.
Another notable discovery was that each participant displayed a unique “yawning pattern.” Tongue movement and the physical expression of yawning varied from person to person but remained highly consistent within the same individual. Researchers compared these patterns to a kind of biological “fingerprint.”
The central question now is why yawning affects cerebrospinal fluid so differently from deep breathing. One possible explanation is that yawning may help “clean” the brain by assisting in the removal of accumulated waste substances. Another theory suggests it could play a role in regulating brain temperature.
Yawning remains one of the most common yet least understood human behaviors. Although it occurs across many species and is often contagious, its precise biological purpose remains unclear. The new study, published in Respiratory Physiology & Neurobiology, adds another piece to the puzzle, suggesting that yawning may be more closely linked to brain balance and nervous system function than previously believed.