MRI scans have given us unique glimpses into the inner workings of our bodies that we'd probably never be able to see otherwise.
Back in 1991, a couple famously had sex inside an MRI scanner, producing some unexpectedly iconic medical images.
Since then, the technology has captured everything from childbirth to bowel movements. While they're not always pleasant to look at, they're undeniably fascinating from a scientific perspective.
Moving to less graphic means, MRI scans have also shown what happens in our brains when we yawn.
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According to Cleveland Clinic, scientists believe the common triggers for yawning are tiredness and boredom.
"Boredom happens when the main source of stimulation in your environment is no longer able to keep your attention," the clinic noted. "This triggers drowsiness by stimulating your body’s sleep-signalling system."
Another theory suggests that yawning is an involuntary action to cool down our brains. The rush of air alters blood flow and potentially lowers brain temperature.
Social factors may also play a role. The 'communication hypothesis' proposes that the contagious part of yawning could be a way of relating to others or signalling shared feelings of boredom or fatigue.
To find out what really happens, researchers from the University of New South Wales in Australia scanned the heads and necks of 22 healthy participants while they yawned and took death breaths, among other things. After analysing the MRI images, the team found a huge difference between yawning and deep breaths.
Unlike deep breathing, yawning sends cerebrospinal fluid (CSF) away from the brain.
CSF fluid is a protective, clear liquid that cushions and nourishes the brain and spinal cord.
Speaking to New Scientist, neuroscientist Adam Martinac said: "The yawn was triggering a movement of the CSF in the opposite direction than during a deep breath. And we're just sitting there like, whoa, we definitely didn't expect that."
The difference between the two bodily actions comes down to the theory that yawning has a more important role in brain function than previously thought. The findings also support the hypothesis that yawning helps regulate brain temperature and that both actions increase the flow of blood leaving the brain.
Interestingly, the study found that each participant had a distinct yawning pattern.
"This flexibility might account for the variations in inter-participant yawning patterns while still maintaining a recognisable, individual-specific pattern; and implies that the patterns of yawning are not learned but are an innate aspect of neurological programming."
They concluded: "Yawning appears to be a highly adaptive behaviour and further research into its physiological significance may prove fruitful for understanding central nervous system homeostasis."