Khaberni - All vertebrates practice yawning, or exhibit a behavior similar to yawning. Until relatively recently, the purpose of yawning was unclear and it remains a topic of debate among researchers and scientists. But why do we yawn? And does it have a benefit?
Andrew Gallup, a professor of behavioral biology at Johns Hopkins University in the United States, told The Guardian: "When I survey the public and ask: ‘Why do you think we yawn?’ most of them suggest that it has something to do with breathing or some way that it increases oxygen in the blood."
This is intuitive, as most yawning indeed involves a clear respiratory component, which is inhaling air deeply. However, what most people do not realize is that this hypothesis has been rigorously tested and proven wrong.
To test the idea that yawning brings more oxygen or expels excess carbon dioxide, studies published in the 1980s manipulated the levels of both gases in the air inhaled by volunteers.
It was found that despite the changes significantly affecting other breathing processes, they did not affect the frequency of yawning. Moreover, there seems to be no systematic measurable difference in yawning behavior among people with respiratory diseases and lung functions, which would be expected if yawning were related to breathing.
This subject piqued Gallup's interest, leading him to study it. He began by examining the movement pattern involving this extended spacing of the jaw accompanied by deep inhalation of air, followed by a quick closure of the jaw and faster exhalation, and he thought it likely had important periodic local consequences in the skull.
Jaw separation can be considered a local stretch, resembling muscle stretching in other parts of the body, and this is exactly what appears to happen as several studies indicate that yawning increases arterial blood flow to the skull, then the venous return (the rate of blood flow from the head back to the heart).
Regulating Skull Temperature
Gallup says: "We can consider jaw separation as a local stretch, similar to muscle stretching in other parts of the body." Just as stretching helps activate blood circulation in the limbs, yawning seems to improve the blood circulation in the skull.
Gallup and his colleagues began developing the idea that yawning helps regulate the temperature in and around the skull.
The temperature of the brain is primarily determined by three variables:
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The rate of arterial blood flow to the brain
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The temperature of that blood
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The metabolic heat production that occurs inside the brain based on neural activity.
Theoretically, yawning could change the first two variables. When we yawn, we take a deep breath of air that moves across the moist surfaces of the mouth, tongue, and nasal passages.
And there are studies confirming this, as the ambient temperature has an expected significant effect on the rate of yawning, increasing when the weather is very warm and decreasing when the air is cooler.
Another Theory
But this theory is not the only one, as there is evidence supporting another theory called the "arousal change" theory, which simply states that yawning helps the brain transition between states from sleep to wakefulness, from boredom to alertness, and so on.
Medical historian Dr. Olivier Walusinski, who has written numerous research papers on the topic according to the newspaper, says: "It is likely that yawning helps rotate the cerebrospinal fluid, which is the fluid surrounding and supporting your brain and spinal cord."
