University of New South Wales Study Finds Yawning Shifts Fluid
Researchers at the University of New South Wales scanned 22 healthy participants and found that yawning moved cerebrospinal fluid away from the brain. Adam Martinac said the team did not expect that result when it compared yawns with deep breaths.
“The yawn was triggering a movement of the CSF in the opposite direction than during a deep breath,” he said in a conversation with James Woodford at New Scientist. He added: “And we’re just sitting there like, whoa, we definitely didn’t expect that.”
University of New South Wales scans
The participants were asked to yawn, take deep breaths, stifle yawns and breathe normally while MRI scans tracked the heads and necks. The researchers expected yawning and deep breathing to look similar on the scans, but deep breaths did not produce the same cerebrospinal fluid movement as yawns.
Both deep breaths and yawns increased the flow of blood leaving the brain. During the initial stages, carotid arterial blood flow into the brain surged by around a third. The finding was not observed in every case, and the effect occurred less often in men.
Adam Martinac on yawning patterns
Martinac said each participant showed 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. “It’s almost like a fingerprint, so you could possibly identify someone just based on how they yawn.”
That pattern may point to a personal central pattern generator, according to the researchers, while the sex difference may have reflected interference from the scanner itself. The team also noted that bigger brains typically lead to longer yawns.
Brain cleaning and cooling
The study adds a possible clue to why humans and many other species yawn, a question researchers have not fully answered. Martinac said yawning could have a role in cleaning out the brain or in cooling it, and he linked the idea to cerebrospinal fluid, which helps the central nervous system run smoothly by delivering nutrients and removing waste.
He said neurodegenerative diseases are associated with an accumulation of waste and added: “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.”
The immediate take-away for readers is that yawning is now tied to a measurable fluid shift the researchers did not expect, and the next step is determining whether that movement has a real role in waste clearance or brain cooling.
