FACT!!! Check out What Happens In Your Body When You Yawn

 

a bit of a mystery, perhaps because it is a low priority for medical research funding, suggests Steven M. Platek, Ph.D., a professor of psychology at Georgia Gwinnett College in Lawrenceville, Ga., who studies contagious yawning.While the medical community has not yet settled on a definitive explanation, the most commonly agreed upon and promising theory is that a yawn is triggered by a rise in brain temperature.
"Brains are metabolically costly," explains Platek. "They're the size of a grapefruit but they consume 40 percent of our metabolic energy. And the brain runs hot."
Researchers have found that yawning has a cooling effect on the brain, preventing it from getting overheated, which can diminish alertness. Core brain temperatures rise when we're tired, when we're unstimulated (read: bored), and among other circumstances such as hot ambient temperatures or infections. And a quick cooling can help us regain alertness.
"Brain temperatures are determined by three variables: rate of arterial blood flow, the temperature of the blood and the metabolic heat production within the brain," explains Andrew C. Gallup, Ph.D., an assistant professor of psychology at SUNY College at Oneonta and a lead author on several studies about thermoregulation and yawning. "So yawning may function in altering the first two variables: increasing arterial blood flow and allowing the flow of cooler blood to the brain."
To answer the question of what happens in the body is fairly straightforward: When you yawn, your mouth gapes open and you inhale deeply, finishing with a short exhalation. During this time, the muscles around your skull contract and stretch and you take in ambient air. New, cooler blood is pushed toward the skull as warmer venous blood is pushed out.
"That action increases cerebral blood flow to the brain and to the skull and, at same time, it forces the warmer venous blood away from the skull," explains Gallup. "The muscle stretching increases circulation to that area."
Secondary behaviors, like stretching out your arms or throwing your head back as you yawn, also function as cooling techniques as ambient air hits the under-arm area, points out Platek. What's more, these full-body stretches prep your muscles for quick action, contributing to the overall push toward alertness that comes from the cooler brain temperature.
In a research review of thermoregulation and yawning published in Frontiers in Neuroscience, Gallup and his colleague Omar T. Eldakar found that rises in brain temperature preceded yawns in both humans and rats, and that brain temperatures went down following a yawn. They also found research that demonstrated how yawns are more frequent when ambient temperatures are high (contributing to high brain temperatures), but actually decrease when they are so high that they exceed internal brain temperatures, thus rendering the ambient air useless in the service of cooling the brain.
Brain thermoregulation has been an important component in the study of human evolution. Platek points to the work of anthropologist Dean Falk, who specializes in paleoneurology and whose radiator hypothesis suggests that our ancestors' brains began to grow to their current powerhouse size after they developed cranial veins that help cool the brain, allowing for the larger, more complex and metabolically costly brains we now possess.
But the thermoregulation hypothesis for yawning only explains the root cause of what's known as "spontaneous yawning." Much of the research done on the subject actually focuses on contagious yawning -- a phenomenon in which we yawn in response to watching someone else yawn, or even hearing mention or thinking briefly about the action. What's more, we are even more likely to yawn when we watch a close friend or family member do so.
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