University of New South Wales Study Finds Yawn Moves CSF in 22
Researchers at the University of New South Wales found that a yawn moved cerebrospinal fluid away from the brain in 22 healthy participants. The MRI scans showed a different pattern from deep breathing, which did not produce the same fluid shift.
Adam Martinac and the MRI scans
Adam Martinac said the team expected yawning and deep breathing to look similar on the scans. Instead, he said, “The yawn was triggering a movement of the CSF in the opposite direction than during a deep breath,” and added, “And we're just sitting there like, whoa, we definitely didn't expect that.”
The study scanned the heads and necks of 22 healthy participants, who were told to yawn, take deep breaths, stifle yawns and breathe normally. Both yawns and deep breaths increased the flow of blood leaving the brain, but only yawns produced the cerebrospinal fluid movement away from the brain.
Yawn patterns in people
Martinac said each participant had a unique yawning pattern that stayed consistent each time. “Each person yawns in a unique way – so the tongue motion during the yawn is different between people, but very consistent for each person,” he said. He added, “It's almost like a fingerprint, so you could possibly identify someone just based on how they yawn.”
The researchers also noted that the effect was not observed in every case and occurred less often in men, although they cautioned that scanner interference may have affected that sex difference. During the initial stages of a yawn, carotid arterial blood flow into the brain surges by around a third.
CSF and waste clearance
The researchers suggested that yawning may help clean out the brain and may also serve a cooling function. Cerebrospinal fluid is the fluid that helps the central nervous system run smoothly by delivering nutrients and removing waste, and Martinac said bigger brains typically lead to longer yawns.
He also tied the finding to work on waste buildup, saying, “Neurodegenerative diseases are associated with an accumulation of waste and the older you get the more waste there can be,” and, “We don't know how strong the link is related to how CSF is cleared, but in the last 10 years there have already been a lot of investigations into that area, and this can be another element.”
For readers following the research, the practical result is narrow but clear: the MRI data linked yawning to a distinct cerebrospinal fluid movement that deep breathing did not reproduce, giving scientists a new behavior to test in studies of brain-fluid clearance.
